The Delightful Children From Down The Lane are five children bent on the destruction of the Kids Next Door Organization and the supremacy of adults over children. They speak in synchronization and stand together in group formation. They are the secondary antagonists throughout the Kids Next Door series. Although the Delightful Children answer to Father, they are seen acting independently just as often. The Delightful Children rarely partake in direct combat, usually sending other villains to do their work and controlling combat machines. Although the secondary antagonists of the show, they make more appearances in the series than any other villain, and more than any character other than the five members of Sector V. They are obsessed with behaving properly and wish to become adults as soon as possible.
Shortly after this is revealed, the Delightful Children are re-commissioned by Re-commissioning Module, restoring them to their former selves as KND operatives. However, the effects of delightfulization were so powerful that any reversion is temporary, and the re-commissioning module's effects wear off during the final battle on the moon base. Sector Z's final words to Numbuh 1 as the delightfulization takes hold again are "Tell The Kids Next Door That we miss them!".
The Delightful Children celebrate their birthday five times a year, as they are technically five people. Each time, they prepare a delicious cake which they intend to eat it without sharing with any other kids and force their "guests" to watch as they do so. Sector V personally attempts to stop them from eating their cake at all costs whenever they celebrate their birthday, which occurs six times throughout the series and composes a recurring storyline, throughout which this simplistic scenario is repeated with several variations and exaggerated to absurd lengths.
In "Operation: C.A.K.E.D.F.I.V.E'.", Father creates a moon-sized ice cream cake for his children and attempts to remove all other ice cream, planning to have all the children in the world watch as they eat the last ice cream in existence. In each of these episodes, the cake is stolen, destroyed or in some way rendered inedible for the Delightful Children, save for "Operation: S.I.X.", where Numbuh 2 is tricked into personally delivering their cake to them. This leads to Numbuh 362 giving the mission to Sector W in "Operation: I.N.T.E.R.V.I.E.W.S.".
In "Operation: F.O.U.N.T.A.I.N.", it was revealed that the Delightful Children were responsible for making Numbuh 1 bald, which was done in such a way that his hair would never grow back. This occurred shortly before he joined the KND, and is never shown and only briefly mentioned, leaving the circumstances of the incident up to the imagination of the viewer.
Their first appearance was in Operation: C.A.K.E.D., the very first episode of the series after No P in the Ool and the first installment in the aforementioned "C.A.K.E.D." series. Their connection to Father was first revealed in Operation: G.R.O.W.-U.P., also the latter's first appearance, in which he gives them use of the "Really Really Incredibly Destructive Machine" and the Age-Changing Cigar from Operation: C.A.B.L.E.T.V.. Using these items, the Delightful Children successfully destroy Sector V's treehouse and turn Numbuh 1 into an adult.
The DCFDTL are obsessed with behaving properly and wish to become adults as soon as possible. In Operation: E.L.E.C.T.I.O.N.S.', they make a deal with Chad to let the students of his middle school enslave the students of Gallagher Elementary in exchange for being "promoted" to middle school level, thereby becoming "that much closer to glorious adulthood." In Operation: F.O.U.N.T.A.I.N., they attempt to destroy the Fountain of Youth in order to prevent anyone from remaining a kid.
When startled, the Delightful Children become disoriented and briefly cease their synchronization with each other. In "Operation: I.T.", the Delightful Children betray Father in order to stop his plan to spread broccoli throughout the world to force feed to children, which even they are against, because they are still children, and even they hate broccoli.
The last we see of the Delightful Children is in "Operation: I.N.T.E.R.V.I.E.W.S.", in which they are on a scavenger hunt to retrieve their cake. When Numbuh 1 returns to the amusement park with Father's pipe, the children begin to battle him for it, and end up on a log-river ride. They get him into a hold and are about to end him once and for all, when Nigel grabs onto a sign as his foot accidently knocks Ashley out of the boat as she lands onto a platform, as the other four Delightful Children fall into a broken part of the ride, and into a deep hole below much to Ashley's horror causing her to break down in tears over the demise of the other four delightful children and she runs away in tears back to the delightful mansion.