#1 Boxcar Children — Henry 14, Jessie 12, Violet 10, Benny 5 (this is baldly stated by the author, something she stops doing just a few books in, which is why I have to compute their ages in other ways.)
#2 Surprise Island — Henry 15, Benny 6 (as stated by the author). Jessie and Violet should be 13 and 11. This is when they spend the summer on their grandfather’s island. Benny has his birthday at the end of the book, so I guess he turned seven. Can I also add: the original illustrations have them all as super, super-blonde, even Henry and Jessie. They’re so blonde that their hair doesn’t even darken with impending adulthood. Yet I am just realizing that these original illustrations clash somewhat funnily with the cover illustrations in the editions that I have, in which all the kids are brown-haired. So on the cover they are brown-haired, inside the book all the illustrations have them yellow-haired. I always imagined them as how the cover depicted them. The discrepancy with the inside illustrations never really pinged at me. It’s only now I’m realizing these brown-haired kids started off as blonde all along, haha.
#3 The yellow house mystery – Henry 16 and in high school, Jessie is also in high school, the ages are given for the younger two: Violet 12, Benny 7. This story begins the spring after the summer of Surprise Island and continues through the early part of the summer. But really, I don’t think the summer could have been more than halfway done at the close of the book. Also, Grandfather Alden’s age is established in this book: he is said to be the same age as the missing man of the book, Mr. McGregor, and Mr. McGregor is said to be 70.
#4 Mystery Ranch — it never gives the ages of the kids, at all! But, it clearly states in the beginning that the summer starts off with a bang. So I’m guessing that means it is the start of a new summer, rather than the continuation of the same summer from the Yellow House Mystery summer. In that case, Henry should be 17, Jessie is 15, Violet 13, and Benny is 8. It’s a little weird, because in the later books, the author starts jamming three mystery books into the span of a single summer — so she can write their adventures while they’re still young enough to be the Boxcar “kids” rather than the Boxcar parents. I guess that early on in the series, though, she must not have been planning to write so many books yet, so there was no call yet to have three mysteries in a single year. Also in this book, they go visit their Aunt Jane “out west” but it never says where, exactly. All it says is they take the 6 o’clock train (from New England), and by early the next morning, they arrive. Well, it doesn’t even say if by 6 o’clock that means morning or evening. So it was either roughly a 12 hour train trip, or a 24 hour train trip. So how far “west” could you go in either 12 or 24 hours by train back in the 1950s, if you started from New England? Does “west” mean Ohio? Chicago? Well, see, it can’t really be either of those unending flatnesses, because the other thing we know is that the ranch where their Aunt Jane lives has mountains around it. Also, uranium is found on the ranch, and from what I can tell, uranium mining happened in places like Utah and Wyoming. So I think, therefore, by “out west” it truly did mean the western US, and not just a few hours west to Pennsylvania.
#5 Mike’s Mystery — This takes place one year exactly after the summer at Mystery Ranch (in fact, they go back to that same ranch). So therefore, Henry should be 18, Jessie 16, Violet 14, and Benny 9. Except remember that Benny has his birthday in the summer: so he should turn 10 before the end. By the way — Grandfather’s ‘FBI Man’ shows up in this book. It is the second time he makes an appearance, after Mystery Ranch. And he is flirting big-time with Jessie. Well, maybe it wasn’t big-time flirting, but Jessie is 16 years old, and he’s showing way too much interest. Jessie does have a crush on this guy, but still, he’s like 25 or 26 or maybe even 30 — he’s a former FBI person who now works for Grandfather. So he can’t be straight out of college, and even if he was, he would still have been too old for Jessie.
#6 Blue Bay Mystery — this book takes place during the school year — so already, the author is cramming the adventures in when she can! No need any more to wait for summers. It starts in December or January, and then the adventure happens somewhere around in February. It is most likely the December directly after the summer in Mike’s Mystery, therefore, the kids are likely still the same age. Nothing is said explicitly: just that Henry and Jessie are both in high school, while Violet and Benny are still in younger schools. Henry, you’ll notice has been in high school for quite a few books now. So just like in the last book, let’s say that Henry is 18, Jessie is 16, and Violet 14; and Benny, who should already have had his summer birthday, is 10.
#7 Woodshed Mystery — this book starts during the weekend before the ‘last week of school’. So at first, I thought that meant, it’s the end of the same school year during which they went to Blue Bay Island. But no! Because Henry is in college in this book, it is stately baldly so at the beginning. Jessie is a senior is high school (and does that mean she’s going to be a senior in the fall, or is this literally her last week of high school?) and Violet is just ready to start high school. Benny is still in grade school. Honestly, it’s becoming clear the author just wasn’t keeping track of things, because there is only a two-year age gap between Violet and Jessie. So how is Jessie a senior in high school (possibly finishing high school) while Violet is just ready to start high school? That’s anywhere from a three-year to five-year age gap. Any case, given that it clearly states that Henry is finishing a year of college — likely his first year — it means that this book must be taking place a year and a few months since the last book. Blue Bay Mystery takes place in February of one year; rather than this book taking place at the end of the same school year, it is taking place at the end of the school year after that. You know, why did the author do that? She could have done a better job of cramming here. Also, the ages are all messed up. Because best guess is that Henry is 19, Jessie is 17, Violet is 15, and therefore Benny should be 10 — except he can’t be 10. You see he’s already been 10 for over a year. He should be 11. But that’s impossible because that makes him only 4 years younger than Violet. So you see, the ages are just messed up in these books. And Violet sure is old for ‘just now’ being ready to start high school.
#8 Lighthouse Mystery — in this book, they drive to the Lighthouse directly from the location of the Woodshed Mystery. So you see no time has passed, hardly — just a bit of time for Aunt Jane to get married to Andy Bean. So therefore, the children are all still the same ages — Henry 19, Jessie 17, Violet 15, and let’s just say Benny is 10, even though there’s a bit of a mess-up there (see Woodshed Mystery). It is still the same summer vacation. There are many references to Henry being in college.
#9 Mountain Top Mystery — this book is ‘early summer’ — presumably the summer after Woodshed/Lighthouse mysteries. Except a few pages after it’s established that it’s early summer, Grandfather says, ‘oh, it’s going to get dark early on these late summer days.’ But no, the author probably meant early summer. The mystery wraps up in just a few days, and then they drive back to the mountain a month later to visit with their new friends. And it was still summer-time when they did that, so the book can’t have started out being “late” summer. Then Henry should be 20, Jessie 18, Violet 16, and Benny is 11. And Henry and Jessie both can read French. I wonder how they managed to learn French in just the last two years or so of high school, because Violet is now pretty old but she did not know French. Well, maybe Violet is still in the beginning classes. At the end of the book, Grandfather announces he has a plan for a fun trip for the following summer as well, but he’s going to keep it a secret till then. John Carter, the FBI man who keeps showing up in nearly every book, spends a whole lunch in this one talking just with Jessie.
#10 Schoolhouse Mystery — it’s early summer again and Grandfather is wanting to take his grandkids on the surprise trip he promised at the end of Mountain Top Mystery. But it gets pushed to the side, because Benny proposes they take a short little trip first. The ages should be: Henry 21, Jessie 19, Violet 17, and Benny 12. And, notice that Jessie is now college aged. But there’s no mention of her going to college. Benny being 12 makes sense, because in this book, they teach school, even Benny, for the kids in the little fishing village they’ve come to visit. It’s a big point of discussion that Benny is a kid himself, too young to be teaching; but Benny is good-natured about it all and he just teaches the littlest kids in the school. They drive back home from the fishing village no later than August 1. John Carter shows up yet again. No pulling Jessie to the side to talk to her, though.
#11 Caboose Mystery — this takes place during the exact same summer as Schoolhouse Mystery. It is stated plainly that it takes place in August. So the ages are still: Henry 21, Jessie 19, Violet 17, and Benny 12. Although recall that Benny has a summer birthday, so maybe he’s 13 by now. Also, Benny is clearly still a kid because in the caboose, he sleeps on the top bunk, and his legs are so short that he can barely make it up the ladder: ‘I can hardly reach these steps with my feet. I guess these footholds were made for a man.’ So Benny is certainly not man-sized yet. And furthermore, when Benny gets lost in the woods, he meets a ‘little boy’ named Charley. Charley is nine years of age. It’s not stated outright, but there’s an implication that Charley is younger than Benny. John Carter shows up at the end of the book — but just to pick them up at the train station — he’s not there to help solve the mystery or anything, like in the previous books. And this is the very last book he’s mentioned. Ever. But what happened? Did he and Jessie fight? Did Grandfather fire him because of that, or had he done poorly at his job? Had he done something corrupt? Stolen Grandfather’s money? Fallen in love with another woman? Who knows — it’s never explained.
#12 Houseboat Mystery — this starts during a very hot July — so assuming it’s the July of the summer after Schoolhouse and Caboose Mystery. Then the ages should be: Henry 22, Jessie 20, Violet 18, and Benny 13. There’s no mention of school or ages for any of the kids. The only piece of information is that they meet a young boy at an auction, a boy who’s even ‘younger than Benny.’
#13 Snowbound Mystery — This book takes place during the fall, and the school is closed for a week due to a fire. They need to repaint it. And Henry randomly has 2 weeks off from college or something. So this is probably the school-year directly following Houseboat Mystery. So the ages should still be Henry, 22, Jessie 20, Violet 18, and Benny 13 — except we know Benny has a summer birthday so they should be: Henry 22, Jessie 20, Violet 18, and Benny 14.
#14 Treehouse Mystery — this one is so good! Two little boys move in next door. They are 10 and 8 years old, and Benny says of them, I just wish they were a little older. So I think that makes sense for a 14-year-old to say. This book also takes place during the hottest of summer. So it must just be the very next summer after Snowbound Mystery. So the ages should still be: Henry 23, Jessie 21, Violet 19, and Benny 14.
#15 Bicycle Mystery — I love a good bike trip. This one is happening the same summer as Treehouse Mystery. As they bike along, they say things like, “Look, there’s the lighthouse we stayed at that past summer” and “there’s where we rode the houseboat.” So from statements like that, the passage of time is recognized by the author. The ages are the same as in the last book: Henry 23, Jessie 21, Violet 19, and Benny 14. We now have three books in a row where the ages stay the same.
#16 Mystery in the Sand — All that is said of chronology is that the book starts on a “hot July day” and it takes place in the span of a single week. So let us just assume that it takes place the same summer as the two preceding books, Treehouse Mystery and Bicycle Mystery. So the ages will still be: Henry 23, Jessie 21, Violet 19, and Benny 14. Although at some point in the summer, Benny has to have his 15th birthday.
#17 Mystery behind the Wall — This book starts by saying that they are just one week into summer vacation. So it has to be the summer after the summer of the last three books. A ten-year-old boy called Rory comes to visit. Benny, who should be 15, keeps saying things like, “of course I can keep up with a ten-year-old boy!” and the two of them spend a lot of time playing telephone (or telegraph) through the closets of their adjoining rooms. Well, I knew of 15-year-olds who played with much younger kids, so I think Benny could have decided to entertain this little boy, too. This book always confused me when I was younger because they kept using “pliers” as they built their telegraph, and I didn’t know what “pliers” meant. Now I do, so it made more sense. The ages of all the Boxcar Kids should be: Henry 24, Jessie 22, Violet 20, and Benny 15.
#18 Bus Station Mystery — This book gives us the exact dates on which it occurs: July 25th and 26th. It starts on the second day of a science fair, and concludes the next day at a town meeting. I really like this one. It’s not so much a mystery, but about saving a polluted river. And they use public transportation! Yes, as part of the mystery at the bus station, they take a few inter-city buses. There are two boys in the book, Jud and Troy, who are described as younger than Henry but older than Benny. Jud and Troy are persistently described as “boys” so Benny should also be young enough to be a “boy”. I think we can assume this is the same July as the summer vacation of the last book. Benny’s birthday is July 15th, so the ages should be: Henry 24, Jessie 22, Violet 20, and Benny 16.
#19 Benny Uncovers a Mystery — The last book that Gertrude Chandler Warner wrote! I always liked this one, too. It takes place all during the month of August. So I think we can assume it happened right after Bus Station Mystery. So all the ages should be the same. The kids are all old enough to have summer jobs. Benny is not old enough to be hired as a clerk in the department store, but he is old enough to be the errand boy. Note that Henry is still studying for his “college” classes (he’s been doing that since Book #7). So the Boxcar Children, who started the series aged 14, 12, 10, and 5, end on this note: Henry 24, Jessie 22, Violet 20, and Benny 16.
Note that the last 8 books take place in a two-year time span! Well-done on the cramming!