It sounds like lactose intolerance to me, but who knows....A friend of mine is severely lactose intolerant. One serving of milk and he bloats right up and disappears to the bathroom for a long time.

You could, if you were so inclined, take him off dairy and see what happens. I would probably buy a carton of soy or lactose free milk and put him on that for a week and see what the results are....just out of curiosity. At least if it's not a lactose issue, then it's been ruled out, no harm done. No child should have stools that loose and plentiful and you're right, it's not normal.

Perhaps it might be a good idea to take a pictures of him over a week's period to show the parents the 'explosions' for themselves? I find it very hard to believe that they're not seeing it over weekends, but perhaps they don't.