Joining strangers at play can be nerve-racking: Will the moms like you? Will your kid fit in? Rest assured, the other moms are thinking along the same lines--though a few preventive measures can't hurt, either.
Start on neutral ground. Sometimes children become possessive or territorial in their own homes. So if you're starting a new group, plan the first few meetings at a park, play place, or the zoo instead.
Set some mom rules. A good one: Find out if the other moms want you to intervene if you see their child misbehaving, or if they prefer to step in.
Hide the contraband. When Amanda Rodriguez (who blogs as "Dumb Mom") hosted her group, her son pulled out his grandpa-given toy revolver and yelled, "Put 'em up or I'll shoot!"--setting kids crying. Lesson: Purge the toy chest before guests arrive.
Think ability, not age. Jennifer Buchet had hoped to bond with a new friend while the kids ran after each other. "But I didn't realize her son wasn't walking yet," says the Frederick, MD, mom. "So while I chased my daughter, she sat bouncing her son--alone."