The Ninja Kids are a group of kids that reside at the waterfall in The Creek. They are obsessed with Japanese culture, meaning things like Manga, Anime, and of course ninjas, and have been seen wielding Bo-staffs and cardboard Shurikens. They refer to the waterfall as "Their Garden" and will attack anyone who doesn't show immediate affection for all Japanese-related stuff.
- Yustice: She is the leader of the group and stays on some rocks in the waterfall. She has dark peach skin, black hair tied with a blue ponytail and a white band on her head. She wears a very warm orange jacket, a pair of dark red shorts and brown sandals with white socks. She also has a round backpack where she keeps two sticks she uses to fight and a western comic book. To let the children in the creek know they have encountered problems, the hair is released.
- Zatch: He is the ninja boy, he is the most enthusiastic about Japanese culture. He has peach skin, completely shaved hair and a white band that covers one of his eyes. He wears a light blue green-collared diver, navy blue pants and dark brown sandals with white socks.
- Prynda: She is the other ninja girl. She has brown skin, long brown hair and a white band on her hair. She is wearing a purple shirt with red sleeves, light purple pants, gray anklets and orange sandals with white socks. She keeps ninja stuff in her pocket.
- "The Final Book" (debut)
- "Escape from Family Dinner" (mentioned)
- "The Invitation" (mentioned)
- "Jacob of the Creek"
- "Council of the Creek" (Yustice only)
- "Cousin of the Creek" (Zatch only)
- "Craig and the Kid's Table" (Zatch only)
- "Tea Timer's Ball" (cameo)
- "Trading Day"
- "The End Was Here" (cameo)
- "In the Key of the Creek" (non-speaking)
- "The Jinxening"
- "The Ground Is Lava!"
- "Council of the Creek: Operation Hive-Mind" (Yustice only)
- "The Ice Pop Trio" (Prynda only)
- "Afterschool Snackdown"
- "The Rise and Fall of the Green Poncho" (Yustice only)
- "Alternate Creekiverse"
- "Winter Creeklympics" (Yustice only)
- "Fan or Foe" (Yustice and Zatch)
- "Capture the Flag Part 1: The Candy" (Yustice only)
- "Capture the Flag Part 2: The King"
- "Capture the Flag Part 5: The Game"