I just discovered the Truth Chronicles series of books for kids ages 8-12 (by Answers in Genesis) and LOVE them! It's a fun story--four kids go back in time--but it throws in lots of fantastic apologetics content. For example, the kids first try to go back 70 million years in the past to see the dinosaurs and it doesn't work (because time didn't exist that far back). Then they try going back 4500 years to see the pyramids in Egypt and end up getting chased by dinosaurs. They're really confused and think the time machine messed up, but the one of the kids in the book is a Christian and explains that there were dinosaurs on earth at the same time as people. Then she has everyone look up at the stars in the night sky and says they learned in science that the stars are slowly changing position and 70 million years ago the constellations shouldn't be in the exact same position as we see them today.
It is a welcome relief to find fun children's books with apologetics content!