Eight years after the events of the Honey, I Blew Up the Kid, ten-year-old Adam just wants to be a normal boy and go to baseball camp. However, his interest in sports seems almost alien to Wayne and Diane, as Amy and Nick, who are currently living away from home, were a Actor and genius, respectively. Wayne has started his own lab, Szalinski Labs, with his brother, Gordon, and they receive tickets to witness a shuttle landing, but Diane interrupts Wayne's message, reminding him that he needs to watch Adam and his cousins, Jenny and Mitch, while she and Patti go on vacation. She also reminds him to get rid of the Tiki Man that she sees as an eyesore, though he considers it a good luck charm (not to mention something that could earn him a fortune one day).
An inventor accidentally shrinks his own and his next door neighbor’s children to a quarter of an inch with his electromagnetic shrinking machine and accidentally throws them out with the trash, where they must venture into their backyard to return home while fending off insects and negotiating hazards.