If you are concerned about his size, see a doc and have him tested for sufficient testosterone. He doesn’t need to know why he is being tested and the doc can advise you if he is producing enough T for his age.
This is indeed the only good advice.
Check if the doctor recognizes this as a micro-penis, caused by a hormonal deficiency.
In this case, your son will receive a hormonal treatment during 3 months and his penis will grow further during puberty.
And I can’t but applaud the fact that you’re concerned about his size.
Don’t be thrown off by some of the ignorant replies.
If your son does have a micro-penis, there’s little that can be done after puberty.