My DS1 has been totally in underwear for at least six months. Abut two months ago he had a stomach virus with vomiting followed by diarrhea. Since that time, his underwear is always damp. It is like he leaks all the time - he doesn't even have to go very much and he'll still be wet.
I am not sure if this is a coincidence or at all related to the illness he had. Have any of your children gone from dry underwear to always wet underwear?