Preventing sun burn

Me, hubby and baby boy are going to our first outdoor party next weekend. He's 4.5 months old. Its been quite sunny and hot in Virginia. My granddad was Irish so me and baby boy have been blessed with that pale skin that burns no matter what. Just wondering what the best sunscreen for babies are and how often should I reapply it? Should I even get him a sun hat? Any other suggestions to keep him from getting crispy. Lol it will be at some ones house so I plan on taking him inside to nurse and such.