Because of the events you just described I would never let a 2 lb dog loose in a park with any other dogs. No way, accidents can happen in a split second and many people can't predict how their dog will act. I am just glad your baby is okay. As small as he is it would not take much for a bigger dog to really hurt him. Maybe the other dog thought your baby was a squirrel.
I can't believe all the people just stood around and watched. Shame on them.