Just when you thought it was safe to let little kids sit through the coming attractions, Steven Spielberg has let the dinosaurs loose. Shelving his usual ”Don’t give anything away” approach, the current trailer for The Lost World: Jurassic Park (opening May 23) is a two-minute ad that teems with prehistoric beasties: A herd of stegosaurs rumbles through the jungle. An angry triceratops rams a truck. A stampede of various species rushes through the rushes. And then there are menacing leaps and lunges by some raptors and a T. rex. All this plus a comforting dose of Spielbergian comic relief. ”Mommy’s very angry,” says Jeff Goldblum, watching a truck get swatted across the screen, Twister-style. As for revealing too much of the plot, this trailer merely implies that this time, the terror isn’t confined to one little tropical paradise. ”Taking dinosaurs off this island is the worst idea in the history of bad ideas,” says Goldblum, ominously. But he seems quite confortable back in the blockbuster saddle.