I just finished a book that I was not the target audience. This was geared to about 9-13 yr old boys.
Enemies and Allies by Kevin J Anderson.
This is set in the 1950's and is the introduction of Batman and Superman. If you have a child that is into comic books or superheroes then this is a good option for them. The reading level (my guess) is about a 7th or 8th grade. There is some history there and they may have questions about Sputnik, McCarthy, and other significant things in that time period. There was not even any kissing just some talk of Superman and Lois Lane falling in love. There are 2 swear words (as far as I can remember). A few spots get graphic about the battles but it is not bad. I enjoyed it and would recommend it to your children if they are into superheroes.