[See: How to Cope With Criticism.]
It's also not clear whether it makes a difference if the bullying comes from a sibling who is much older or around the same age -- or whether it's between sisters, brothers or sisters and brothers, Tucker said.
But she and Copeland both said it's safe to assume that parents' reactions to their kids' aggression matters. "Let your kids know this is something you won't tolerate," Copeland said. Even if the bullying doesn't stop, he noted, kids may get a lot of comfort knowing they can turn to their parents for help.
"If there's no real escape for kids," he said, "that could make it a lot worse."
The American Academy of Pediatrics has advice on dealing with bullying.
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