Joseph Henderson, co-director of Durham's Walltown Children's Theatre, is asking for our help. "As you know, Durham is in a crisis," he says. "The number of violent crimes being committed by our young people is growing in frequency. Too many teenagers are dropping out of school and are being lost to drugs, gangs and prison." To get this message out, the Walltown Children's Theatre will present Bangin', an hour-long play that shows the horror of being in a gang. The first performance, on Wednesday, July 17 at 7 p.m. at the Carolina Theatre in Durham, will be preceded by a 45-minute rally on the plaza. The play will be performed again July 18-19 at 10 a.m., noon, and 7 p.m. Call 286-4545 for details.