My pick would have to be the A Whole Nother Story trilogy, in which (spoiler warning) you can only travel back in time. But because time is in a loop of sorts, if you go before the beginning of time, you will be at the end of time. From there you can go back to any time you want to. And time paradoxes cannot be produced. Plus, your memories from the previous timeline exist as well as the memories from the new one.
The Old Powder Line. I read it as a kid in the 80s and it blew my mind - it was the first book I read in one sitting as it was so engrossing.
A kid finds an extra platform at his local train station and a steam train arrives in it. Essentially, this steam train drives back in time and when you get off you take over your body further and further back in your timeline.
It’s actually quite trippy and creepy for a children’s book.