We were at a Sizzler one night when a group of children acted as you describe. I felt so sorry for the poor guy who was sitting with his wife and daughter not far away. He looked amazed when he saw our family with five children and realized our children had been so interested in their food that he had not even noticed they were there before.
Years ago I was with a group at Shoney's and there was a group of parents having a night out with their kids and their hellions were running ALL OVER the restaurant. The parents were totally ignoring them. FInally, one of their little darlings who looked to be 5 or 6, took a hot pot of coffee (about 1/4 full) from the waitress station and was walking around offering to fill customer's cups. The waitress grabbed the pot and child, took her to the table and raised HELL at the parents, who got P.O.'d at the waitress for making a scene! Our group thanked the waitress afterward.