Pink and Blue Time Travel: Nick Baron, Glory's End (Robert Silverberg's Time Tours (New York: Harper Collins,1990).
What puzzles me sometimes is the precise ways in which a children's science fiction novel can be bad. This novel manages to be both demanding and patronising all at the same time. It's demanding because it is asking children to assume understanding of the grandfather paradox clearly enough to see that it can be used as a weapon (kill your own grandfather and your enemy can't get to to you) and to set up endlessly coiling time loops in which some people retain the memory of the changed times and others don't and to communicate these clearly and effectively and embedded within the story...
And at the same time to use the word-substitution method of worldbuilding (...the pod drew up beside them, Rafe looked at his chronometer... etc), and to posit a social system identical to ours in which every single female character's place in the book is justified by a romantic attachment (so that men want to go back into history to see great events, while a woman wants to go because she has fallen in love with the diary of a dead soldier).
Cognitively, the book is very interesting: unlike many from this period it makes intellectual demands but no emotional demands. Much more like the earlier fiction,
Just after reading this I read Joanna Russ's The Two of Them..., a book in which the world is built in moments of shock, and of amused observation. There is nothing in this book that an intelligent thirteen year old girl couldn't grasp. Of course, that might be a very good reason for keeping it out of her hands [g].