Harry and the Dinosaurs at the Museum by Ian Whybrow
Harry's sister, Sam, is studying the Romans, so Mum and Nan take them both to the museum. Sam starts working on her project once they arrive, but the dinosaurs start to get bored and also a very tiny bit naughty too. So Harry teaches them some fun tricks, like climbing, sliding, and playing hide-and-seek. But soon they're having so much fun that they get lost! Will Nan know where to find them?