What the song did thay sing after making a fire

The answer is Kumbaya

Kumbaya or Kumbayah, on Gullah it means Come By Here. It is an African-American spiritual song from the 1930s. It enjoyed newfound popularity during the folk revival of the 1960s and became a standard campfire song in Scouting and nature-oriented organizations.
The song was originally associated with human and spiritual unity, closeness and compassion, and it still is, but more recently it is also cited or alluded to in satirical or cynical ways which suggest false moralizing, hypocrisy, or naively optimistic views of the world and human nature.

Here are the lyrics they sang in the movie:

Kumbaya my Lord, Kumbaya
Kumbaya my Lord, Kumbaya
Kumbaya my Lord, Kumbaya
O Lord Kumbaya

kumbiya (spelled that wrong)