He's going to be what he is going to be, and it works out fine for everyone in the end.

Still, your question seems odd. Isn't almost everyone hung small as a kid? Thing usually change at puberty. That happens a different rates. I graduated from high schoool with a guy who was less than five feet tall. I saw him again recently and was shocked to find that he was now the same height as me. (6'3") You get the analogy, I'm sure.