Birthday Party Game ideas 4yr olds in a park?

My son is turning 4 in two weeks. He is having a dinosaur themed party. We have about 25 children coming so we have decided to hold the party in a local park that has Dino inspired playground. We have hired a Dino jumper. We want to do a couple of games but I am having a hard time figuring out what to play. All I have so far is a Dino egg and spoon race. Any ideas?