I've seen this behaviour in dogs. Medium-sized dogs like German Shepherds (aka Alsatians), Dobermanns, Rottweilers, etc. tend to attack smaller dogs like toy breeds and small children. The owners are encouraged to socialise them but sometimes it doesn't work.

There aren't many cat-owners in my country. Because of the superstitions still surrounding cats and the crime-rate, people prefer dogs. So I don't know much about cats. I don't think I've ever seen kittens in a pet store either. Pups, turtles, fish, love birds. Never kittens.