This waterproof shower cap from Magic Collection is sized for kids and designed to keep hair dry during bath and shower time, with a soft, gathered band for a comfortable, secure fit on a child's head. Magic Collection's own guidance includes a genuinely useful safety note worth passing along: supervise children while the cap is in use, and don't let kids play with it unsupervised, since any bath-time accessory made of a flexible waterproof material carries a basic suffocation risk if treated as a toy.
Beyond that, it's a simple, practical accessory -- rinse and hang it to dry after use, and wash it periodically to keep it hygienic for repeated bath-time use.