[JoeyP]

Yes, this isn't dominance He is afraid of your son
and it probably isn't anything that your son is doing on purpose

Yorkies are little dogs
and kids being kids run and jump and do things that kids do
This can be interpreted as danger to a new puppy

So he's going to back away when your son comes near him
The way to make friends is have your son feed him
when the puppy is sitting with you on a couch have your son sit down near you

have him not greet or look at the puppy and at minute intervals have your son give him a treat and you say Good Boy!

The have your son do it on his own

You want the puppy to know that good things happen when your son is around