Uncle Grandpa is a show with the style of insanity and ridiculousness, creating its humor. It is not ridiculous to the point where it is just an insane series of colors and shapes, attempting to amuse. It still has characters and tells stories with them; it’s just that they are not realistic. The show still tells interesting stories with their characterizations.
I have noticed that it actually takes a lot of notice and pre-awareness on the part of the viewer to find the show appreciate able. The show does just seem random, but there is more than just Uncle Grandpa and impossible insanity.
Uncle Grandpa is the main character, is the Uncle and Grandpa of everyone in the universe, and is a magical being who goes around and helps people. That is the extent of the explanation given on this, and it is taken as premise for the rest of the show. He is magical in the sense that he follows a completely ridiculous and non realistic set of rules for reality, such as duplicating himself, elastic arms, and teleportation. Thematically, his magical-ness is to take advantage of being a cartoon character, resulting in humorous, albeit unrealistic, situations and approaches to problems. The show very much has this unreal nature embedded into all of the adventures shown. For example, to help one kid be better at video games, Uncle Grandpa literately asks out loud for Uncle Grandpa to shrink him down and place him on the kid’s face, in order to get to his brain. At this point the camera view zooms out to a second Uncle Grandpa at a computer with a Photoshop like application, who acknowledges the first Uncle Grandpa, and edits them down to size, and drags them to the kid’s ear. Then the view returns to the first Uncle Grandpa, who tells the second to “add some lens flair” at which point such appears on screen. Again, that is the extent of explanation given on how all such was possible and the episode proceeds with Uncle Grandpa shrunken down inside the kids head.
While Uncle Grandpa may seem idiot in all of this, he is actually competent in helping others, and has caring morals, but again does so through his ridiculous ways. His job of helping others is shown to be important and successful; he even journeys into danger to help a kid, saying that he hasn’t lost a kid yet.
The other characters actual exist with this and the ridiculousness of Uncle Grandpa is actually noted explicitly by the others. These characters are: Belly Bag, a living phanny pack that assists Uncle Grandpa. Pizza Steve, an exaggerating cool guy living slice of pizza. Mr. Gus, the green dinosaur, is often the straight man to Uncle Grandpa, pointing out the insanity. And Giant Realistic Flying Tiger, who looks exactly as her name describes but is friendly.
For example, in one episode Uncle Grandpa is incapacitated, and the others have to take his job helping people. The episode focuses on how they will do so, since only Uncle Grandpa has these magical abilities, noting the normal unrealistic nature of the show.
In all of this, the show does have positive morals of friendship, helping others, being yourself, imagination, and fun.
In short, I hope this description is helpful in reviewing the appropriateness of this show, in that it is descriptive of it and explains what it is. Mainly, it takes a strong awareness of detail, and like of ridiculousness to find the show entertaining, beyond just amusing colors and shapes. It also requires a comprehension of reality and the unreal, and if teaching unreal things is your concern than that would be a good reason to teach this comprehension to your children or wait until they are more intelligent/developed to appropriately expose them to this show.