Lol. Yeah, those sleepy nappy changes were the worst. The first one I found very affronting. Until that point I though he had been only very moderately bestowed. He was about 11 months old and WHAMMO! I had to wait for it to go before u could put the nappy on (bending it down just DIDNT work, and made hubby cringe).
Now, at 3 and being TT, he gets a full on erec.tion every time he goes poopy. Every. Time. It's a bit odd.
The other day I found him exploring it, and like a pp had to stifle a giggle and explain that it's bedroom business.
Op, I would *worry* but maybe bring it up at next health check/drs appt/immunization etc...