I think if your parents are digging their heels in then it becomes simple - if they want their grandchildren to visit then the dog is locked away. I have a big dopey dog that I trust as well as I would trust any dog with my kids and he is allowed around my girls all the time, but when there are other kids over he is locked away. I feel sorry for him being excluded, especially when he doesn't understand what's going on, but I would rather that than him or a child gets hurt