ABC said Tuesday its radio unit plans to buy Philadelphia station WWJZ-AM from Mt. Holly Radio.Financial terms weren’t disclosed. The station will broadcast Radio Disney, the live, 24-hour radio network designed for children under the age of 12. ABC Radio Networks said Radio Disney is now in 16 of the top 20 U.S. markets, including the top five. It wants to be in all 20 by the end of 2000.