Hi Elaine,
My son is 2 1/2 and is a semi only child. My step daughter lives out of state and comes to visit once a month for a weekend and stays with us for the full summer, the rest of the time my husband and I joke that we have 2 only children. Actually, I had a question back to you, has your son always played so well independently? My son can play independently but 90% of the time he needs constant attention he is very demanding! Although he definitely has a wonderful imagination and he amazes me everyday, I'm thinking even as only children they all have there own quirky personalities. And I agree with your friends, first I don't think you have anything to worry about and second I'm also a little envious!
From another Mom of an only child.
Also, my husband is an only child and says he loved growing up as an only child and getting all of his parents attention to himself. As an adult he is a very confident, intelligent, caring man who loves his family.