There is a caveat, or at least used to be, I don’t know if it has been changed: If your son is approaching teen years, his sub account will ALWAYS be a subaccount, so when he leaves the nest, he won’t be able to take that account with him, get his own PS+, etc…
When my son left for the service several years ago, we found out this harsh reality and he lost all of his hard earned K/D ratios =)
EDIT: Speiling