The Ankle-Biters are a group of evil babies that were born in the Memorial Hospital. According to their leader, they want to band together to stop older kids, which they consider to be adults, from treating them like babies. They are able to talk by stealing teeth from older kids. They formed a huge caterpillar-like robot that attacked Sector V when they wanted to take their teeth. Their only appearance was in Operation: D.I.A.P.E.R..
They consist of:
- Baby Jackson, the leader of the group that stole Numbuh 5's teeth.
- A blonde-haired baby that drives a race car and attacked Numbuh 4 with his drool.
- A baby that drives a plane and blinds Numbuh 2 with a dirty diaper, causing him to crash.
- An unseen baby that hit Numbuh 3 with his rattle after she saved him from falling off the treehouse.
- Triplets who split a set of stolen teeth amongst themselves.