From Muppet Wiki

Junior is one of four kids who went camping with Grover in Sing-Along Earth Songs. He seems to have had more significance than the other kids. He threw a can into the water before learning not to throw things into the water, and when he got tired of carrying his water canteen and asked Grover to carry it (along with all of the campers other heavy equipment), he considered pouring the water out just to make it lighter for Grover.