You can do it on how they extincted
I am looking for the same thing for my son. I think we are going to do one on how they can calculate the size of the dinosaur by their tracks.
You can buy Dinosaur Fossil Kits from the market for your science fair project. I am giving you websites for some details.
If you could change his mind he could do something like pollution of the air soil pollution water pollution how does an electric guitar make noise