I remember this song being popular with Belfast (N Ireland) children on group bus trips. It is easy to imagine it started when some child actually needed to pee and said "stop the bus, I need a wee wee" and the other children started up a chorus and now it is sung, to the same tune, over a wide area

Michael Lavery, what are verses 2 and 3 then? Or do you mean the fourth (final line) of the verse?