Marshmallow Kids are six marshmallows that live in the Candy Kingdom. They appear in the episode "Susan Strong." They refuse to run away from the Hyooman tribe, stating that "The Marshmallow Kids never run from a scrap!" Jake then accidentally sets them on fire as they run to fight. This sets the Hyooman tribe's hats on fire. The Hyoomans then rip off the hats, revealing they aren't human before fleeing. The Marshmallow Kids then shed their burnt skin. When Finn asks if they'll be alright, they reply that they'll just be gooey for a while.
The Marshmallow Kids play a major role in "Scamps", where a gang of four of them—Gary, Johnny, Sunshine, and Hugo—are caught by Finn and Jake trying to scam Starchy. After learning of their underprivileged street background, Finn takes them on a camping trip in the wilderness to try to show them about life beyond scamming. They grow to respect him and as of the end of the episode, they appear to be attending the Candy Kingdom Preschool.
They appear to be rivals with the Pup Gang, whom they refer to as the "Notorious Poop Gang".
They are particularly brave for Candy People, seeing as they ran right into the fight.