The Silver Platters
Iconic '70s sitcom The Brady Bunch (1969-74) sets its sextet of siblings a-singing in the "Amateur Night" episode (01/26/73). The kids want to engrave a silver platter for their parents' anniversary gift, but Jan miscalculates the price. So they enter local TV show The Pete Sterne Amateur Hour (MC Pete Sterne played by Steve Dunne) to try and win the $100 first prize money. They perform the Archies-esque "It's a Sunshine Day" to audition, but sing "Keep On" on the show. They come in third but learn some kind of valuable lesson about some heartwarming thing, I'm sure.
You really should know this, but the Brady kids were: Marcia (Maureen McCormick), Jan (Eve Plumb), Cindy (Susan Olsen), Greg (Barry Williams), Peter (Christopher Knight) and Bobby (Mike Lookinland).
In reality, the producers herded the Brady brood into the studio to record no less than four albums of pop fluff and covers to cash in on the show: Christmas with the Brady Bunch (1970), Meet the Brady Bunch (1972), The Kids from the Brady Bunch (1972) [containing the above songs], and The Brady Bunch Phonographic Album (1973). MCA released an, ahem, "best of" compilation CD in 1993, It's a Sunshine Day: The Best of the Brady Bunch.