My son had the same thing happen,  I think.  Is your son overweight? or are they "breast buds" ---kind of hard under the nipple.  My son got the later when he was 8 or 9, I can’t remember exactlty.  He was being undersuppressed so they increased his cortef and the buds went away.  If your son is overweight then it is probably due to being overweight.

 

Good luck to you.