Try Smithsonian Global. They have a website set up by Smithsonian Folkways to allow people to download the entire Folkways catalogue. £10-00 per record or 99c per track. They have quite a lot of kids/camp stuff. I'd especially try searching for Ella Jenkins, Leadbelly, Pete Seeger and Ed Badeaux through their search engine.

http://www.smithsonianglobalsound.org/