For those of you who think there is terrible parenting or whatever going on here, I think you're being ridiculous. The "hitting" in this video is just one boy basically just TOUCHING his brother. He's not doing it to be mean. At that age, babies haven't yet developed the muscle tone to make gentler, smoother movements. Jerky, "rough" movements make up most of what they are able to do. Also, they haven't yet developed enough intellectually to understand that they're doing something unpleasant to someone else. The Mom handled it exactly the way she should have, with gentle correction. If the boy being "hit" had reacted to it in a way that showed he was really upset, I'm sure the Mom would have separated them and made sure it didn't continue. As you could see, though, the boy being "hit" really didn't seem to mind very much. Babies are pretty resilient. Getting a whack on the head from your twin brother, when both of you are 15 months old, isn't going to do you any damage.