2 books · Ages 6–9 · Chapter Books
Xtreme Sports Skills is a 2-book series for ages 6–9 by Lisa J. Amstutz. Each book stands alone — start anywhere.
Start anywhere — each book stands alone.
That said, Supercross Bumps and Jumps and Supermoto: All-Around Skill and Speed are great first picks.
No particular order needed — browse and pick what catches your eye.