Returning from a playdate, you notice that your 5-year-old has a certain guilty air. Soon it's clear why: His pal's favorite Star Wars action figure is hidden in his fist. Your grade-schooler is old enough to know better, says Bhavin Dave, M.D., associate director of the Infant and Toddler Mental Health Program at Children's National Medical Center in Washington, DC. "[But] he's probably not headed for a life of crime...even if it's a pattern." To avoid a repeat offense:

Ask What Happened Though all signs point to petty theft, give your child a chance to explain. Kids this age are often honest when asked directly, so don't bother being coy.

Express (Calm) Disapproval This age group has an innate sense of fairness, so you can say that stealing hurts people -- including the thief, who gets in trouble and could lose a friend.

Talk About the Rules The lesson is simple -- no stealing. You can let first offenders off with a warning, but mention that you'll punish future slips.

Make Amends Karen, a mom from Seattle, made her otherwise well-behaved daughter go return a toy she'd swiped from a friend. "She was mortified," recalls Karen. "But it never happened again." Apologizing can be stressful, so you can offer to do it together or even role-play beforehand.

Look More Closely If this happens often, talk to your doctor: ADHD, mood disorders, or other problems may be at play.