I'm almost thirteen, I'm gonna be working for the teens sooner or later, so I figure why not sooner!
~ Numbuh 12
Numbuh 12 was one of the female operatives at Numbuh 86's slumber party in Operation S.L.U.M.B.E.R. When the Teen Ninjas attacked, she betrays the KND and gives the Kids Next Door Code Module to Cree, stating that she was almost thirteen and believed that she would have to start working for the teens sooner or later, thus making her the youngest person to work for the teens. Numbuh 86 claims that she was her "only real friend".
She also had a cameo in a flashback in Operation M.A.U.R.I.C.E, appearing as a younger version of herself with pigtails rather than a ponytail.