That entry is the 2006 television film:
The film reveals that was once Numbuh 0 , the greatest operative in K.N.D. history. He defected not out of evil, but out of resentment: his parents (The Grandfather and Grandma Stuffum) forced adulthood upon him, and the K.N.D. failed to save him. Father’s villainy is a tantrum against the inevitability of growing up. Codename- Kids Next Door - Operation Z.E.R.O. -...
Numbuh 1 stood at the helm of the Bridge, his small hands gripping the railing until his knuckles turned white. On the primary monitor, the transmission from Deep Sea Lab 9 was flickering out, replaced by a hauntingly familiar silhouette: a man in a sharp suit, his eyes glowing with an ancient, flickering orange light. That entry is the 2006 television film: The
When (Grandfather's son) mistakenly brings him back to life using a recommissioning module, Grandfather quickly betrays the modern villains and begins transforming both children and adults into "Senior Citizombies" —mindless, elderly slaves. As the Kids Next Door (KND) organization collapses under the zombie onslaught, Numbuh 1 (Nigel Uno) must embark on a desperate mission to find the legendary hero, Numbuh 0 , the only one who ever defeated Grandfather in the past. Major Revelations and Lore failed to save him
When the villainous Father finally acquires the ultimate weapon to erase childhood forever, Sector V discovers that the key to stopping him lies in the long-lost legacy of their own founder—and the heartbreaking secret buried in Father’s past.
In one of the most poignant scenes in children’s animation history, Monty Uno realizes the truth. He looks at his son not as an annoying kid, but as a fellow operative. The line— "I remember... I remember everything. The treehouse, the missions... and you, son. You look just like me in my prime." —is enough to bring any long-time fan to tears.
The story opens with an impossible crisis. The legendary —Father’s own elder—escapes his containment in the Arctic Prison. A tyrant from World War II, Grandfather possesses the power to turn anyone over 13 into a mind-controlled, decrepit "Senior Citizombie" and anyone under 13 into a mindless, obedient toddler. His goal: Total conformist stagnation.