soiling the pants at age four is not consider "normal" so you need to discuss this issue with his pediatrician. he could be "stool-holding" -- a common problem with busy children who don't really want to take the time out of their busy day to have a bowel movement. they would rather suppress the urge but as you know "poop happens" after a period of time when he can no longer hold it. over time his distal rectum can become quite dilated so he may need some help in the way of stool softeners and watching him like a hawk to make sure he isn't doing the "hide and poop" game.
is it normal for a 4 year old boy to still be soiling his pants? he is fine with peeing during the day and overnight.