Its clear that it was all set up. The screams of kid are not actually the screams but he was trying to copy 'something' Also you may listen the laughter of guy who was making this movie. The kid is not 'really' trying to get rid of Dog rather he is more interested in playing game.
It seemed to me that the kid rather enjoyed it as he was not trying to get away. raped? I think not! he never said no or down, or leave my pooper alone
It looks like a setup - initially, the kid positioned himself in a doggy manner which he knew provoked his dog and sure it did. Anyways, seems like both enjoyed it.