Wayne Szalinski is a crazy scientist who invents a miniaturizing machine that is so powerful it only blows things up. When the kid next door hits a baseball through the window and it lands in the path of the machine's laser, it begins working. Wayne's two kids plus the two kids next door end up becoming tiny. Wayne accidentally sweeps them up and puts them out with the garbage, so the kids then have to travel through the thick grass back to the house, while braving giant bugs, sprinklers and a lawn mower.