In an ideal world, I would agree with the advice to address the kid directly. This is what I hope other parents would do if my child were going around hitting people. However, I once had a very bad experience with a similar situation. I was standing in line at a cash register when a small boy belonging to the woman in front of me turned around, looked me in the eye, punched me, and then laughed. Startled, I said "Excuse me!" The woman turned around and started yelling at me: "Mind your own business! He didn't hurt you! If you had any kids you would know better!" (Ironically, I was at this time the parent of a child exactly the same age as the one in the store, but my daughter wasn't with me so the woman couldn't know that.) Since this incident, I have tried to avoid speaking to other people's children for any reason unless I know the parents or it is absolutely necessary to prevent serious harm. On the rare occasion when I do have to speak to a child, I always say something like, "Uh-oh! I don't think your mother would like to see you hitting people," rather than just ordering the kid to stop. So I would advise going to the owner rather than dealing directly with the child or the parent, unless you are certain that the parent won't react negatively.