A fight begins when a 5-year-old boy bounces a building block off his friend's head. A friendship ends after an 8-year-old girl calls her friend ugly.
No need to worry. At some point, experts say, all kids act mean--particularly with their peers, because the behavior can be easy to get away with. In fact, aggression in the early years is a positive sign that the child's mind is developing; it's also a way for children to test their social skills.
But, experts say, adults should worry if:
* The behavior is frequent. Continued aggression almost ensures a child will have few or no friends. "Don't worry if a child comes home crying because he got in a fight with a peer. This happens to everyone," says Kenneth Dodge, psychology professor at Vanderbilt University. " Do worry if he comes home crying every afternoon." Or every week.
* The behavior consumes hours. Children are forgiving. One minute a child can be hitting and howling, the next happily playing with a toy. A child who dwells on not liking a friend is stuck in anger and "will have a harder time learning how to get out," says Nicki Crick, psychologist at the University of Illinois. "Especially if this way of thinking becomes a habit."
* The behavior is cruel. "Kids can be sadistic," says Alayne Yates, psychiatry professor at the University of Hawaii. "Kids can become so enraged that they'll do anything to hurt someone." For example, a child might stab a peer with a pencil or knife. He might beat a dog. Or destroy a sibling's favorite toy.
Most children 8 and younger are unaware of how cruel they're being, Yates says. But that doesn't mean that at 10, they'll suddenly realize and quit. "It becomes ingrained, and often it progresses," she says. "It's almost impossible for a child like this to have stable friendships."
* The behavior alarms another adult, such as a teacher or neighbor. Sometimes, parents are oblivious to a child's friend troubles. At home the child's an angel; outside he's a meanie to peers.
* Sometimes, shyness warrants concern. Aggression is still a factor with a shy child, says Ronald G. Slaby, psychologist, author and a lecturer at Harvard. But rather than a child becoming aggressive, he's a victim to peers' aggression.
"Many shy kids have a hard time making friends," Slaby says. "They're usually the ones that classmates repeatedly pick on. When confronted, they don't stand up for themselves or show any pride or dignity."
Parents should be concerned when shyness causes a child to be overly anxious, withdrawn or inactive.
Otherwise, a child can be shy and fine, adds Dr. Harold H. Bloomfield of Del Mar, psychiatrist and co-author of the relationship book "The Power Of 5" (Rodale Press, 1995). "Shyness is not a disease," he says. "It can be a sign of great creativity and inventiveness, something most peers respect."