Is he having major accidents or just little ones? If it is just little ones, then I would suggest the Imse Vimse trainer. They are terrific and look just like underwear. However, they are not SUPER absorbent. They are true trainers and are best for kids who might leak a little but don't have massive flood like accidents.
For the heavier wetter child, I would suggest the Happy Heiny's trainers. They come in three options 1) snaps on both sides, 2) snap on one side or 3) no snaps. The no snaps look just like underwear. You can stuff them with as much absorbency as you need depending on your child.
WAHM to three, all natural, organic and sports-obsessed boys:. MDC7 for 7% off at www.cottontailbaby.com or www.mamaclothonline.com for all your cloth diapering and natural family living needs: