The Trailer Folk are a mother and son that live together in a trailer in the human world.
During Mike Wazowski and James P. Sullivan's skirmish with Randall Boggs over possession of Boo in Monsters, Inc.'s doorwarehouse, Randall managed to briefly seize control of the child, until she utilized a baseball bat and other items from her room to fight against the color-shifting monster. Sullivan grabbed Boggs by the neck, and, with the assistance of Wazowski, threw him into another door into the trailer.
When Boggs emerged on the other side, he was greeted by the Trailer Folk, and the son called for his mother, claiming another alligator had found its way into their trailer. The mother then proceeded to beat Boggs with a shovel, while he cried in pain.
Behind the scenes
The Trailer Folk's trailer also appears in A Bug's Life while Flik goes to the big bug city located underneath it. Additionally, a Pizza Planet delivery truck can be seen to the left of the trailer, reflecting its appearance in the aforementioned film.
According to the Monsters, Inc. commentary that is included on the film's DVD release, the son's model is identical to that of the simulation kid, but with the addition of a cap, while the mother's model is the same as well, but with a "bun" placed on the head.