George and Harold were usually responsible kids. Whenever anything bad happened, George and Harold were usually responsible.
I am not the target audience for this book. However, much like Goosebumps, I cannot help but have a lot of gratitude for a series which got so many kids reading.
Harold and George are a couple of Ohioan pranksters who write, illustrate, distribute and sell homemade comic books called "The Amazing Captain Underpants" about a superhero in his skivvies who fights crime and monsters.
Mr. Krupp, the school principal and is the boys' enemy. He is not merely a put-upon principal struggling to control two misbehaving boys, but he is genuinely a bad person. For instance, when he gets proof of the boys' misdeeds on tape, he blackmails them into becoming his personal slaves - making them wash his car, clip his fingernails and paint his house.
The boys, chaffing under this treatment, decide to hypnotize Krupp using a mail-order hypno-ring.
They use the ring to hypnotize Krupp into believing he's Captain Underpants, and the rest is history.
...
Although this book is aimed at young children, there is some great humor in it for any adults who may be called upon to read it aloud.
For instance, the boys attend Jerome Horwitz Elementary School. Jerome Horwitz is the man who played Curly in the Three Stooges.
Other scenes play out to both kid and adult humor, like when
"Mommy," said a little boy sitting on a bench, "I just saw two robots driving a van with a guy in his underwear hanging off the back by a red cape, pulling two boys on a skateboard behind him with his feet."
"How do you expect me to believe such a ridiculous story?" asked his mother.
This is funny because his mother is reading the "Tabloid Times" with a headline of "Bigfoot Gives Birth to a 200 Pound UFO Baby."
Or when a sign on the police station reads:
POLICE STATION
Back in 15 minutes
Please don't commit any crimes 'till we return.
Thank you.
So it's not all poop jokes and diaper jokes, is what I'm saying.
Tl;dr - Not as bad as you are anticipating. Birthed a lot of readers. Also contains humor adults will find funny.