'A KID'S LIFE' What would ''Sesame Street'' be like without Oscar the Grouch? A possible answer is ''A Kid's Life,'' which recently opened at the York Theater Company. Although this production also has upbeat songs, cheery lessons in the workings of the world and adults dressed in oversize fuzzy costumes, it features little of the inspired wit and occasionally acerbic observations that have made ''Sesame Street'' so ingenious. While clouds sometimes gather over that neighborhood, the nameless little town in ''A Kid's Life'' is virtually all sunshine, all the time.

Not that children under 7 are likely to mind. Even though they were absent from the performance I attended (bad weather had caused school audiences to cancel), it was easy to imagine them enthralled. ''A Kid's Life'' follows a small boy named Zack (Carlos Avilas, above right) and his dog, Starsky (Yoav Levin), as they meet Zoe (Ashley Wallace) and introduce her to the neighborhood. Over the course of an hour little theatergoers have the opportunity to bat balloons through the audience, clap and sing to the music and shout instructions to the actors.

The show, which sometimes seems more like a participatory concert (Cynthia Riddle and Peter Hunziker's book is thin), embodies a certain 1960s feel. You can easily envision the folksy pop score by Corey Leland (also the lyricist) being belted out by the Association or the Turtles. Peace signs are flashed at the end, and the action includes tree hugging (literally), as Zack and Zoe meet Bart (Joshua Greenwood, above left), an orange tree.

The most hilarious moment soon follows, as the huge Starsky ambles over to Bart and serenely lifts his leg. I don't know if this was in the script or the idea of the director, Keith Markinson, but it displayed a refreshing irreverence the show could use more of. Oscar, would you consider visiting? (Through Jan. 13 at St. Peter's Church, 619 Lexington Avenue, at 54th Street, 212-935-5820, akidslife.com; $20 to $60. Holiday week schedule: Saturday at 10 a.m. and 12:30 p.m.; Sunday at 12:30 p.m.; Monday, Wednesday and Thursday at 11 a.m. and 2 p.m.)

LAUREL GRAEBER