I can assure you that if you ask any of my children if they need to "void" that's exactly the expression you'll see on their face. I doubt they even know what "urinate" means. (They probably ask, "I'm a what?") How old was the kid? If he's young enough to refer to it as "emptying the teapot" I doubt he'd be old enough to know what "void" and "urinate" mean. It sounds to me more like a clash of extremes, too technical v. too babyish.