FRIEND'S ARRIVAL SUDDENLY MAKES SIBLINGS ENEMIES

 Your kids get along great until they have friends over.  Why do kids turn on each other when their buddies are around?

 Siblings are natural rivals for household resources, parental attention, and family standing, as well as social dominance within and beyond the family circle says Carl Pickhardt, author of  "Why Good Kids Act Cruel"  (Sourcebooks, $14.99)

 Three Cs--comparison, competition, and control--are the lifeblood of sibling rivalry, Pickhardt says, and are generally heightened when the siblings are the same sex and close in age. 

 "A visiting friend can add fresh fuel to the rivalry between the kids around a series of hard questions," Pickhardt notes.  "For example, who will control the play, who will the friend like best, who will take sides against whom, who will be included and who will be left out ?"

 Parents can resolve these sorts of questions before the friend is invited by setting ground rules such as these:

     Everyone will be included in the play.

      Everyone will be treated well in the play.

     Everyone will have a share in creating the play.

 Parents may notice that siblings, as well as friends, often get along best when a parent isn't hovering, because the kids aren't vying for an adult's attention.  So you might consider securing agreement on the rules upfront, then keeping a safe distance.