Infinity Ring Book One: A Mutiny in Time, by James Dashner is the start of a seven book series, to be written by six different authors (ala the 39 Clues series). The premise of the 39 Clues was a treasure hunt; the premise of this series is a time hunt!
Dak and Sera are best friends, leading more or less ordinary lives at Benedict Arnold Middle School. Except that they aren't exactly ordinary themselves--Dak has an over-the-top fondness for historical information, and Sera is rather brilliant when it comes to physics....And there's the fact that their world is rather different from ours--it's a somewhat dystopian version of reality, with the sinister SQ controlling things, and odd moments of dissonance, known as Remnants--strange sensations of missing someone or something. And finally, there's the fact that Dak's parents have almost completed a time machine, and Sera is able to finish the job.
Before the fact of time travel can sink in, Dak's parents have whisked them off for a jaunt to Revolutionary War America (and geez, if I were time travelling, I think I would try to go somewhere where there wasn't a war going on. Like the middle of an Iowa cornfield in 1950. I'd work up to war gradually). But in any event, it goes wrong, the parents get left behind, and Suddenly! Dak and Sera are being introduced to a secret cabral of Hystorians, who are most keenly interested indeed in the time machine.
Because, you see, the time machine is necessary to fix history. The Bad Guys have broken the past, disrupting the natural flow of events (did you pick up on the Benedict Arnold middle school, for instance?). And because Dak and Sera are the only ones tuned into the time machine, they have to become agents of the Hystorians, travel back to the broken bits, and fix them, and if things aren't fixed, the present is going to go even further down the drain.
There are some things that will make the time mission easier--technology solves the language problem, and the prep. work of the Hystorians over the centuries (agents from the past, waiting in their time period for time travellers to come) provides some guidance once they get there. But just as the explanations are winding down in the Hystorian Headquarters, there's an attack from the SQ bad guys, and the kids must quickly travel into the past to start their work. Chance pushes one of the Hystorians, Riq, into their journey--he's an older kid, and not at all warm and fuzzy.
So there Dak, Sera, and Riq are back in 1492. Columbus is about to set sail, and the famous mutiny that displaces him from his destiny as "discoverer of America" is about to take place....And that, I think, is enough summary!
Well. It is interesting, and exciting, and with lots of middle grade appeal (for, perhaps, the ten year olds, give or take, in particular. The adult reader might find the characters annoying at times (Dak and Riq both grated on my own nerves, with their know-it-all, antagonistic jockeying for relative status), and might be thrown out of the book occasionally with questions about temporal paradox and historical accuracy. But of course, this isn't for the older reader. The history seemed to me accurate enough (though, of course, accuracy is tricky here, cause of history have been warped) that I had no burning issues with it, and the characters might well be more warmly embraced, or at least better tolerated, by the younger reader....
This was one of those time travel books when it is all made easier than it would be if you were time travelling in real life. Technology and insider helpers are key to the kids' success, and they are able to pass successfully as ship's urchins. The result is that this is more of an adventure story, propelled by time travel, than a time travel story, propelled by adventure. Which is fine--the former category almost certainly has broader kid appeal than the more introspective, character-reaction focused, type of story.
To add to the enjoyment of the target audience, there's an online game component. I tried it out, and didn't get very far, and don't actually have a useful frame of reference with which to form an opinion. It seems fun, and not without educational value...I was worried that each physical book granted access for just one user--there's a map tucked into the book that has an access code, but there is a way for multiple users of the book to set up accounts. Librarians might want to black out the access code on the map, and perhaps write a little note where the map goes saying that if you go to the web site, you will find a way to access the game by referencing particular pages of the book.
Note on divesity: The game shows images of the characters--Dak white, Sera Asian, and Rak as clearly black (he is described in the book as dark of hair and skin). I am going to have to go back to see if there is textual description of Sera (hmm, long dark hair was all I found; will keep checking); Rak is still a secondary character in this book, so I'm not putting this on my list of multicultural sci fi/fantasy just because of him...maybe in later books, he'll move to primary status!
Final note: it is a bit ironic, at first glance, that Columbus not discovering America is something broken that needs fixing, because of course there were many, many unfortunate consequences to that discovery. However, in the alternate history it gets discovered anyway by the same ships, just with different guys (who are not any more altruistic) in charge.