THESE ARE PARLOUS TIMES FOR THE young, as evidenced by a pair of youth-oriented programs this week. In " 'Teers in the Hood," a grim episode of The New Adventures of Captain Planet cartoon series airing Friday, May 13 on TNT (6:30 p.m. ET), TBS (7 p.m. ET) and the Cartoon Network (7:30 p.m. ET), the Planeteers go back to high school after a popular teacher is gunned down in a cross fire between two teen gangs. Stranger Danger is a news special on Nickelodeon (Tues., May 17, 8 p.m. ET) that looks at both the scary reality of and the hysteria surrounding child abduction in this country. With Linda Ellerbee serving as host, the program offers sensible tips for avoiding dangerous situations. Parents of younger children may want to seek out Smart Kids, Safe Kids, a similar tape that many video rental stores lend out free as a public service.