Travellers' cant. Travellers arrive at an illicit camp, but awake in the morning to find their old pony impounded by the farmer. They ransom it and move on, finding water for the children
The song is macaronic, combining Travellers' cant with English. This shares some lyrics (references to "tent-rods, ridge-poles, and kittles") in the first verse with "The Atching Tan Song (II)", but they seem otherwise separate.
An "atching tan" was a stopping place; it was common practice for Travellers to camp in an unauthorized place, then let their horses into a farmer's field after dark with the intention of retrieving them before dawn. Often as not, they were caught and the horses impounded. - PJS