The Marshmallow Kids are six delinquent marshmallows that live in the Candy Kingdom. They first appear in the episode "Susan Strong" when they refuse to run away from the Hyooman tribe, stating that "The Marshmallow Kids never run from a scrap!", and Jake then accidentally sets them on fire as they run to fight. This sets the Hyooman tribe's hats on fire which makes them rip them off, 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.
- A female marshmallow kid can be seen to the left of Fionna on the cover of Adventure Time with Fionna and Cake Issue 1.