I know this doesn't always hold true, but...many well hung kids have a well hung
dad, so i think that the parents should almost expect it.
There was always a lot of subtle hinting and teasing about
the well hung men in my family (it wasnt blatant, just my dad joking around a bit).
My brother was a chip off the old block, although i'm average.

The parents of my godchild noticed the big endowment of their son when he was
a teeny child, so...i think some parents know already.