Happy from The 7D is full of energy and loves to play music and entertain people.
In early episodes of The Amazing World of Gumball, Darwin is almost unfailingly energetic. He becomes less so later on, but he's still usually more upbeat and optimistic than Gumball.
Buster Baxter from Arthur is easily the most fun loving out of Arthur's friends. Whenever he's feeling down, it's usually for a pretty good reason.
Aang certainly qualifies, particularly in the earlier episodes. He does undergo some serious Character Development, though, once he discovers the gravity of the circumstances he and his friends are in. His Keet-ness is taken up to eleven when an Earth Kingdom general, who is attempting to invoke the Avatar State for military use, has him drink the Avaverse's equivalent of Red Bull.
Good Lord, Bloo from Foster's Home for Imaginary Friends is nearly the epitome of this trope. While he is a self-centered Jerkass and is often a Bratty Half-Pint, he is very energetic, hyperactive, and excitable at the same time. In fact, in one episode, he dances insanely. Sometimes he even borders on the Cloudcuckoolander territory.
GIR from Invader Zim. His electronic robot voice coupled with his bizarre enthusiasm for everything makes him a very notable example.
Clancy and Ping from Julius Jr. Both of them are generally excited over the littlest things.
The Mask: The Mask is this as he is very energetic, fun loving and impulsive along with acting like a kid as well which makes him very well loved and liked in Edge City.
Same goes for K.O. from OK K.O.! Let's Be Heroes. He's absolutely adorable, almost always smiling, and his near-constant cheerfulness, energy, and optimism lifts the spirits of his two cynical best friends, Rad and Enid.
Jet from Ready Jet Go! is this to the extreme, always being loud and cheerful.
Sanjay from Sanjay and Craig has a high-pitched, bombastic voice and is shown to be a very cheerful Nice Guy.
Scooby-Doo: Scrappy is this. While all of Mystery Inc. (With the exception of Shaggy and Scooby) are definitely into solving mysteries, Scrappy's sheer enthusiasm stands out.
The titular character from Steven Universe definitely fits, as he's a nigh-perpetually cheerful, fun-loving, hyperactive All-Loving Hero.
The Evil Midnight Bomber What Bombs at Midnight from The Tick, who is constantly rattling off conversations about his evilness to no one in particular and has severe trouble not bursting out phrases like "Down with government!" during normal conversation.
Wander from Wander over Yonder who is always happy, fun loving and upbeat.
Cliff, one of the two judges from the talent TV show "Wow!" from World of Winx is a definite keet, since, unlike his grumpy fellow judge Margot, he is excited by what the contestants bring to the show.
Everyone from Word Party falls into this trope, but Kip is the most prominent example, as he is a perpetually excitable, hyperactive, and energetic Cloudcuckoolander.
Jack Spicer of Xiaolin Showdown becomes this temporarily upon being turned good by one of the artifacts. He spins and twirls, all the while talking about how being good puts the entire world at your fingertips. Needless to say, This freaks out the heroes and they want desperately to turn him back into the Big Bad they know.
