An interesting notion, I was reminded of a movie a number of years ago, Time Cops was the title I believe. There was actually an agency that would send officers back in time to correct timelines that were being changed. These time riders are young people, teens to early twenties, who seem to be the only team organized to fix timelines that someone may have tried to change.
Liam, Maddy and Sal, all of whom have been saved from death to join the team. They all come from different periods of earth's history. Foster who is the senior (as in senior citizen) member is the one who saves them and trains them for their job. They also have the assistance of a clone who is something of a superman.
The team exists in a future earth. There was another team but it apparently was wiped out, thus the need for a new team. They find that sooner than they think two of them are sent back along with Bob, the clone to stop a change which will be apocalyptic unless they stop the ones who are playing with time.
The characters are interesting and very different from one another. They are young an unsure of what they are supposed to be doing but Foster assures them they will be fine. What he initially does not tell them is that he is dying and they will be on their own.
They become more self assured as they go along, however, their first mission makes them question whether they should have been involved, maybe dying would have been better. There is not that much action so the book does move a little slowly, still it was enough to keep me going. I had to know whether there was a trip back home or not. Since this is going to be more than one book, I will be interested in seeing how they do, now that Foster has gone to live out the last bit of time he has left.
The next book will be travel to the prehistoric past, this could be interesting. Reminds me of the BBC series "Primeval". Maybe I like Time Riders because it keeps reminding me either of television series I like or a movie which was so so. Maybe it just grew on me. Anyway, if you like time travel, try this one out and see what you think.