Need help with Birthday Centerpieces, please?

Ok... I am one of those 'spaz' mom's that everything has to have a rhyme, reason and theme... lol My little Riley is turning 1 in a week and I am going thru my last bit of 'decorating' for his party. His 1st birthday party is going to be a 'farm theme. My best gf is making his cake, a barn shaped sheet cake decorated as a barn... with cupcake farm animals for the kids. I bought all the farm theme plates, napkins, and such. And hubby and I rented a portion of a lake for the day. So we will be under a pavilion, with a swimming beach and playground for the kids. But decorating a pavilion can be quit