The funny, smart people behind Nickelodeon's animated ''Rugrats'' series know their dual audiences, juxtaposing the blithely self-absorbed parallel universes of small, diapered children and their large, Dockered parents. This first feature-length production does more of the same, advancing the TV story line with the arrival of baby brother Dylan (''Dil'') for natural-born toddling peer-group leader Tommy Pickles. The inevitable heavy-handed life lessons about jealousy and responsibility are doled out -- courtesy of writers raised with Dr. Spock and Mister Rogers' Neighborhood as spiritual guides. But the creative team also dispatches overeducated parenthood and post-permissive childhood with wry, observant wit. (One sitcom-influenced cheat: The moms, as a group, are far more practical than the dads.) Guest voices by Margaret Cho, Tim Curry, Whoopi Goldberg, Andrea Martin, David Spade, and Busta Rhymes up the hipness quotient; among the hospital-nursery babies, listen for Jakob Dylan, Iggy Pop, Lou Rawls, Lisa Loeb, Patti Smith, and the B-52's.