Many folk songs have been copyrighted and played with by "collectors."

Yes, EB, many examples, but not necessarily this one.

'My 95 year old mum swears she sang this when she was 3 year old (1928)' Okay, Jude. My mam's 97 and she would probably swear the same. But unless you can come up with actual documentation 1939's a very plausible date.

When people compose these simple little ditties they don't necessarily take too much notice of reality. They're just for FUN!