Meet Police Officer Ninja and learn how to overcome your fears! I'm Police Officer Ninja, Strong and brave, Helping folks out, Quick to save. Life is hard! It's even harder for children who are just trying to figure things out. The Ninja Life Hacks book series is: Geared to kids 4-10+ Perfect for boys & girls Early readers Grades K - 6th grade and up Excellent resource for counselors, parents, and teachers alike Collect the entire Ninja Life Hacks book collection and box sets!.