Strange Dogs and control the kids!

I was out walking with a client last week who owns a very large male Rottie. We were at the park and working on loose leash walking when from out of nowhere a young child comes up and starts hugging this big boy. Mom kind of sauntered up behind her child, and stood their watching. I held my breath and then stepped in between the dog and the child, concerned even a well behaved dog like this Rottie was has a limit. I