I've never seen these in any stores, but they are nice and old-school, no?
Hanna Andersson has nice organic ones for your little precious. My friend Paula tells me they don't have any elastic so they are extra comfy on that soft skin.
C-Man has a few pairs of white boxer briefs too. To be like the big boys.
There's also this option that I posted about way back when. I know C-Man will want all those *other* undies as soon as he finds out they exist, but until then, the underwear aisle is yet another aisle I can't walk down with him in the cart. Ignorance is bliss, people.