Well, I was being slightly facetious. Of course you wouldn't pee in a kid's mouth if there's warm water handy. But I'd rather use pee than have the child rip the skin off his tongue.
Pee is mostly warm water, usually available, reasonably sterile and nontoxic. In a pinch, you can even drink it. So yeah, I have heard stories of dads using pee in this situation. At least one dad, I'm pretty sure.
And as for the bull, I don't think I'd worry about pee at all.