Eighty percent of U.S. children have a sibling. Siblings can be sources of companionship, play, and joy—as well as jealousy, rivalry, and aggression. A national survey found that one-third of U.S.

As an only child, I was in for the shock of a lifetime when my children first started properly fighting. Of course, I knew siblings fought – I grew up alongside other kids and watched their close (and ...