Homer injures himself while playing basketball at the Springfield YMCA, and needs surgery. While recovering at home, he finds he is good at caring for pets and at babysitting the Flanders' children, so much so that he starts a daycare center which gets him nominated for a Good Guy award for service to the community. But Bart and Lisa feel neglected through all of this, and are determined to thwart his award campaign.
The family goes to the YMCA to attend one-time-only free classes, along with many other Springfieldians who admit they would never return to the YMCA and pay for any of the regular classes. Lisa takes gymnastics (and gets yelled at by the Russian coach for being too old), Bart gets tricked into taking an etiquette class by a black man dressed as a gangsta rapper (who happens to be the husband of the prim and proper etiquette teacher), and Homer participates in a basketball class for men over the age of 35, but suffers a torn ACL after a dunk attempt end with the backboard crashing down to his leg. After Homer gets his surgery, he is told to Dr. Hibbert that he cannot go to work, and he must stay home. Homer finds himself extremely bored, even going so far as attempting to cross-breed Santa's Little Helper and Snowball II. One evening, Ned wants Marge to watch Rod and Todd while he attends a Chris Rock concert (that he misinterprets to be an abbreviation for a Christian Rock concert), but Marge is out identifying a body (which ends up being a very much alive Hans Moleman while everybody thinks is really dead) so Ned asks Homer instead. The kids like having Homer take care of them, which allows Homer to establish his own day care center.
Homer starts a day care center (under Marge's ownership), "Uncle Homer's Day Care Center", to entertain himself, but makes Bart and Lisa feel like outcasts by ignoring them, giving Bart's jacket to Milhouse forcing them out of their bedrooms for a film crew that is making a documentary about him, and having them work long hours at night to cut out felt hearts in his honor. The daycare center is wildly successful, and Homer earns a nomination for the "Good Guy Awards" ceremony. For the ceremony, Bart and Lisa splice in home movie footage of Homer as his worst (passed out on the floor drunk and almost naked during Christmas, losing Maggie in a poker game, and chasing Bart down the street while wielding a chain mace) to prove to everyone that Homer's nice guy persona is a sham. The audience becomes outraged and Homer angrily strangles Bart on stage. Everyone in the audience becomes horrified by Homer's behavior, and decides to prevent their kids from being watched over by him. Homer escapes from the ceremony with all the kids in a van, until he crashes the van into a tree, and tries to escape before Chief Wiggum stops him. After three mistrials, Homer apologizes to Bart and Lisa for neglecting them, and promises to take care of his own children (including the perpetually-ignored Maggie) instead of the neighborhood kids.