If your dog should start to mount on you or a kid, or another dog he is trying to assert himself and be dominant. You should immediately stop this behavior. Say NO! Off! whatever he happens to be straddled on at the time. Correcting the problem when he is this young will help it from being a major problem. I also think puppy class is in order for you both. It also sounds to me that he is bored and taking his frustration out on his toys. I would sign up for puppy class so he can burn off that extra energy and also bond with you stronger. He needs to be taught what he can and can not do NOW! This will make him a well adjusted pet once he knows the rules etc.
During the spring especially I have 4 dogs all neutered/spayed and
they mount each other sometimes. Actually it is pretty funny seeing
the oldest dog who is almost blind mount my female only he doesn't know
which end is which. She will just walk away and he will still be going at
it. Neutering will help curb his aggresssion with other male dogs and not
be so territorial. But as far a hormones go remember he can still smell a
dog in heat from his nose not his testicles! The urge will always be there
even after neutering your dog. This is a natural thing and do not be afraid
of it or your dog! Good Luck
PUG