I think it's more that a child can pick up a gun and shoot someone. As in the possibility exists that they can pull it off. Or you can train a child to take the shot and they can. The wizard's don't have that advantage as they need to want to kill someone to pull off the killing curse not just accept it.
Nice. But I think it goes to Hufflepuffs. They seem like the sort to work hard and party all night. Like Oil riggers home from work.