I've only recently heard this song. Although I don't know it's origin, it's my impression that it's only a children's song because it's been robbed of it's original meaning. I think it's a negro spiritual, not an underground railroad song. In fact, there are no extant underground railroad songs. "Follow the Drinking Gourd" is the product of Lee Hays of the Weavers. In all probability, it only goes back to the 1940s.