I wasn't sure what to do in this sort of situation. It was something where you read about it in a parenting magazine, but never expect to actually see it first hand. I ended up throwing Ella's cool cup out (Paul thought we could just take it home and toss it in the dishwasher since it has a sanitizing feature), but I just preferred to toss it. Later while we were still there the older brother had also butted in on a game Paul was playing and then the little girl again tried to interrupt Ella as she was playing another game, all the while the parents were still sitting in their corner munching on pizza.
I probably should have said something to the parents, but they seemed like the type of people who could care less about the situation and just think that I am some crazy over protective mom. So we left the place knowing that another kid is growing up not learning proper manners and there is nothing we can do about it except to teach Ella and her future brother that there are just some people like that in life and we will have to just go on living our lives and accept those people for who they are.