I will likely know if my future sons have unusually large or small penises. We are nudists. Perhaps my children will be like I was, and suddenly want to hide their bodies from everyone when they hit puberty. I certainly won't stop them.
By the time my father got to know me, my breasts had developed pretty well. I was nine. When they kept growing, he became sporadically protective, but not nearly as protective as my mother.
My mother had a reputation for being over-protective of me. When boys would approach me, their friends would ask them if they knew who my mother was. Once they knew, they would no longer speak to me. I wish I was making this up.
On the other hand, this is the same mother who saw that as a baby I was stiff, where most babies are limber. When trying to make me stretch at home wasn't improving my flexibility, she enrolled me in ballet, and made me stay there for tn years despite my utter lack of talent for dance. Years later she confessed she did it because she was afraid I wouldn't be flexible enough to be a good lover, and she wanted my life to be fulfilling and my experiences to be well-rounded.
I do think some parents think this way about their children's bodies, and only hope most of the ones who do are as benevolent as my mother.
So. When the time comes, and I notice my boys' developing bodies, and if I see anything unusual, what will I do? I doubt I'd say anything. I doubt I'd see their erections, anyway. They will have been told by their father that erections, though natural, are private, and likely taught to cover erections when not alone. I'm hoping that we will have fostered an environment where questions can be asked, even embarrassing ones. I expect my husband to teach our hypothetical boys to stretch and kegel, and encourage them to spend as much time masturbating as they like, so they can learn about their bodies as we learned about ours. But I would want these things regardless of their penises' sizes. Outside of any issues of selecting appropriately modest clothing, and explaining why clothes need to look a certain way, I really can't see why a well-hung child needs different treatment.