My (Canadian) mother (born in the '40's) used to sing this song to me when it was time to brush my teeth. I've never met anyone else who's heard of it.

Who's in the bathroom
Hanging on the wall
Who's in the bathroom
Long, lean and tall?

Who's in the bathroom
Who do you think?
Why, it's your friend
With the bristles on the end
Johnny To-o-o-oth
Brush 'em up, brush 'em up,
Brush 'em up, brush 'em up