I would look into helping my son "be bigger" ONLY if it proved to be absolutely medically necessary--i.e. due to some kind of hormonal imbalance, etc..
Most ideally however, I would hope to be the kind of father that would encourage honest, candid dialogue first with my son about ANYTHING sexual which he may have on his mind. ( I never had this opportunity for fatherly guidance, wisdom, and advice. And, I've paid the price, too, later in life.)
The sooner a son realizes he's not by himself in questioning his penis size, sexual prowess, and other sexual issues; that other guys ALSO have these concerns, the healthier that young man will be emotionally AND physically. His dad is the best one to tell him this, too.
Having a dad ready to listen and "counsel him" is worth much more than any methods, potions, or chemicals to try to help him "grow it bigger".
If only we men could find a way to be more accepting of our bodies the way they are, then we could (perhaps) convey that message to our sons by our own example!
Boys have always had difficulties transitioning physically and emotionally into manhood. But these days? ...With culture and the internet making this process especially difficult? I stay amazed at what I'm reading about (and still learning about!)....often within this very forum.
As I'm getting older, it saddens me what young men are thinking and trying to "adjust to" these days.