I could not have written a better book for my bone-obsessed 4 (almost 5!) year-old if I tried. He's so fascinated by bones: how they break, how they fix, and how they grow. This book includes actual x-rays on almost every page! The x-rays are on transparent x-ray paper so you can view them against the blank paper behind them, or hold them up to the light. It includes broken bones, growing bones, teeth, pregnancy ultrasounds and more. My kid is obsessed, and can now talk knowledgably about MRIs.