Not very nice of me to say so, but it was funny. Animals are animals, and at that age you should of know better before trying to touch some unknown one.
It didn't look like he was beat to blood though, and I can imagine it hurts. You could tell what's coming if you deal with horses all the time, but I bet it was an unpleasant surprise for someone with no experience. Lesson learned I guess.
Wild horses? Either way, common sense would say stay away especially with babies there. He could not see that pinned ears are a sure sign the mare is pissed? Some people are totally clueless when it comes to reading animal behavior. Again, common sense would say stay away. He is an idiot. He is lucky it was not worse.