I think that's just what kids that age do. If it were you standing on his blanket, or another child he'd probably hit you/them also. At this age they really test their boundaries, etc and I've found they hit, scratch, pinch in order to test those boundaries. You just have to teach them to be nice to the dogs/cats just like they would anyone else. We don't have any pets, but my 17 month old hits my brothers dog also.