If they are school age, they are old enough to scare the heck out of them. LOL Also, if they go to school, they do have to behave there, so thery understand rules, tell them yours. I love my 2 little grands, 8&5, but they are like wild things when they come here. I lost my "grandmas cool" once, really yelled at them and it scared them so much that now I usually only have to threaten them a few times to calm them down. LOL