Madeline and the Bad Hat by Ludwig Bemelmans

A new little boy moves next door to Madeline, and she and the girls think he is a bad kid. The boy, Pepito, taunts the girls. Ms. Clavel tries to help find an outlet for the boy's energy. Pepito learns from the error of his ways when letting a cat out of a bag backfires, and he gets attacked by dogs. He becomes really good, but the girls miss the old Pepito. He goes back to his old silly ways, but he promises never to harm animals ever again.