I don't have a problem dealing with other people's kids. At the hospital there were some that were making a mess of the waiting area and being noisy. Families are waiting anxiously to hear if their loved ones survived neural or spinal surgery and these brats are treating it like Playland.
I turned to one behind me, put on my "Don't Fuck With Me" face and said, "Stop it. Right. Now." The kid sat down and shut up, shortly after that the parents took them out of the room. I have even had kids run past me and grab my leg to swing around and make the corner while they chase each other. The second time the little shitstain tried it I sidestepped and he slammed head-first into a table, fell down and started bawling. The mom gave me a dirty look, like it was my fault I didn't want her sticky little yuppie-larva grabbing at my clothes.
Then I took her place in line when she went to get the kid.