A Child number makes for easy identification, obviously. Similarly, when I hear a number I often identify this with a hymn tune (Hills of the North Rejoice = No 64) even when I haven't sung it for decades.

However, the question was about the tune. Which tune? There are several. I personally prefer the Whittingham Fair one referred to by Jim though probably the OP wants the Carthy / Simon one. Google is your friend.