I saw this movie on TV in 1985 or so.
It's a comedy Western from maybe the 1960s or 1970s, a little boy (12 or younger) is behind the bar in a saloon and a bad guy orders a beer. The boy pisses in a glass (either to prank the guy or just because he needed to go) and the bad guy is served this glass and takes a sip.
I think there's a group of children who are the heroes in the movie.
Something in the vein of a Disney family movie, "The Apple Dumpling Gang" (1975) http://www.imdb.com/title/tt0072653/
looked like a promising candidate.