All he does is drink milk, sleep, and he never brushes his damn teeth, er, gums. If I did that, you’d be able to smell me over your modem.
WAG: Milk mostly consists of fat globules in emulsion, and very little sugar. Common oral fauna doesn’t break down fat well, thus there isn’t much decay and stuff going on.
Also, he doesn’t yet have halitosis-causing bacteria in his mouth. You get those from other folks. Don’t let him tongue kiss anyone yet