C.G.
I'm curious why you won't let him have milk at night. My daughter is 18 months old and we still do 3 cups of milk a day. One in the morning, one before nap, and one before we brush teeth. I think they still need 20-24 ounces of milk a day at that age. Also any chance your son could be diabetic? To be that thristy is pretty odd I would think? I would pay a trip to the doctor. But I think he probably needs more milk.