Amadscientistgrandfatherinventsagenetictransformationmachineandhis4yearoldgrandsonaccidentallyturnshisbodyintothatofa30yearoldman.BabyBobbyescapesandrunsaroundtownashissiblingstrytocatchhimbeforetheirparentsgetbackfromvacationANDbeforethebadguysgettohimfirst.Themachineisworthalotofmoneyandtheyonlyhaveadaybeforethemachinelosesitscapabilitiestochangebabybobbyback.