He's a puppy AND he's small. Small dogs get "freaked" (for lack of a better word) by kids because of their fast and quick movements. I'm sure your son didn't do anything to the puppy..it's just the reaction to him moving the way kids do.
This is why it is recommended time and time again for people with very young children to get a different type of dog. With that said, YOU can work on this and make it work. It will just take time to teach him and acclimate him. It's only been a week - this means in the beginning, the puppy was still "not comfortable" as it takes about a week on average for them to relax and feel at home in a new place. Now, he's comfortable and is showing that the quick moving small human is scary a little. Just reassure and always be there when they are in the same room together. As he grows older, they will both adjust to each other.
I understand that you human child must always come first, but don't give up too fast on your pup. He needs you to show him the way
