Adults whose frame of reference for teen idols is Frankie Avalon or the Monkees should get hip to the New Kids on the Block, who star in a pay-per-view cable concert on Dec. 7. The New Kids will be up to their usual tricks performing catchy hip-hop pop and treacly ballads, dancing in impeccable unison. But these are teenybop kings with aesthetic curiosity and a conscience. Head Kid Donnie Wahlberg recently expressed his admiration for the dense music of rap's Public Enemy, not exactly a fave-rave act among the New Kids' predominantly white, female audience. And the Kids took time out from merchandising themselves to give benefit concerts on Oct. 12 and 13 for a worthy if low-profile cause, Amnesty International's efforts in Chile. It seems as if the New Kids are the thinking girl's teen dreams.