A man is walking through the park with his young son one day when they come upon two dogs screwing.
The man hopes his kid doesn't ask, but sure enough he does.
"Daddy, what are those two dogs doing?"
"Well son, they are making puppies"
Amazingly enough, this answer was enough for the boy and they continue on their walk.
The following saturday morning dad and mom are in bed making love when junior walks in on them.
He asks
"Daddy! What are you and mommy doing?"
"Well son, we are trying to make a baby"
"Well, roll mommy over because I want a puppy instead"