Curious Pictures was the production company behind the ill-fated Jay Ward homage, Sheep in The Big City, in 1999 for Cartoon Network. Three years later, the company rebounded with their most successful entry to date.
Codename: Kids Next Door was the result of a CN viewer poll, and launched in 2002, beginning a 6 year run. As is typical practice for CN and competitors Nickelodeon & Disney Channel (and their attendant sister networks), the series was shown on weekdays even though not enough episodes initially were made to warrant a regular weekday schedule. It did air on Saturdays for a while on Kids' WB! as a temporary replacement series, but the programmers there didn't promote it appropriately enough to warrant keeping it there long-term.
The concept is simple. The Kids Next Door is a worldwide organization of pre-teens who battle teenagers and adults. In a sense, it's a satire of typical police or spy dramas, and it works because it brings children's imaginations, particularly the game of Cops & Robbers, to life.
The core team in the series operates out of Sector V in an unnamed city. The 5 members are a culturally diverse crew--2 Americans, 1 Japanese, 1 Australian, and 1 Englishman. Their most recurring foes are the Delightful Children From Down The Lane, a quintet who speak entirely in unison, whose father figure is presented as a personification of the Devil (and voiced by Maurice LaMarche using his Orson Welles/Brain voice), but is secretly the uncle of Numbuh 1. Go figure.
Here's the open:
Of late, CN has brought the series back as part of its rebooted & revamped Cartoon Planet anthology package.