The dad might have not know you said no and once you told him told his kid to go away. Some kids have disabilities that make them extremely compulsive causing them to ignore command such as no it sucks but in the end the dad dealt with it and kid left you alone. If that’s big of deal tell the parents instead of the kid as then it’s someone of authority can take control. It sucks that bothers you. Maybe hold cards on what to around service dogs. I’ve never had problems with kids. If they come up to me I just move my dog under me and tell them he has an important job and had to focus. I say you can look at him but don’t took him. If your dog is medical alert than I would stay outside of the doctors office and ask them to come get you. You can sit in a low traffic area or an area that can hide your dog away. Sorry you having that problem.