Why you shouldn’t ignore it : you know that you have to step in when your child punches a playmate, but you shouldn’t disregard more subtle aggressive act, like shoving his brother or pinching a friend. “if you don’t intervene, rough behavior can become an entrenched habit by age 8 . plus, it sends a message that hurting people is acceptable,” say parents adviser Michele Borba, ED.D., author of Don’t give Me that attitude! : 24 rude, selfish, insensitive things kids do and how to stop them.