As parents help their little ghost, goblins, fairies and princesses put the finishing touches on their Halloween costumes this week, the staff at Rock Creek Park is busy preparing for more than a thousand trick or treaters at the annual Trunk or Treat festivities. With Halloween falling on Saturday, organizers are expecting the biggest crowd to date. "The last two years, we have had close to 900 children and hope to see even more this year," said Buffie Hamil, programs coordinator for the park system.