Codename: Kids Next Door Season 1 Episode 13

In "Operation: G.R.O.W.-U.P. (Getting Really Old Will Upset Plans)", the Delightful Children From Down the Lane get help from their father to destroy the KND once and for all. Not only do they almost defeat their archenemies for good, but they also manage to make Numbuh 1 an adult and they demolish their tree-house, too. Now with their leader gone (now that he is an adult, he went to get a job) and their faith, too, the remaining KND are forced into an all-out war with their most dangerous foe of all time.