Dinosaurs after dark - Jonathan Emmett

Bobby wakes up in the middle of the night to hear something "sneaking softly past his window". He looks out and see

A HUGE ENORMOUS DINOSAUR!

He follows out into the night and finds a host of other dinosaurs playing in the city square, using the buildings as swings, slides and trampolines.
When they spot him, they threaten to eat him if he tells anyone about their existence, but Bobby promises not to tell, so they all end up playing a game of hide and seek together instead.
Bobby runs off to hide and finds a great hiding place in a dark tunnel. He sits and waits for the dinosaurs to find him