I'm by no means an expert on living by the beach, but I thought I'd share what worked for us, We stayed in Florida for a week and thankfully nobody got a sunburn. With the girls we were diligent about applying Babyganics sunscreen 20 minutes before they got in the water and then reapplying after about 2-3 hours.
I bought both Layla and Mariam sunhats from Old Navy but I only got them to wear them for a little while before they would just tear them off.
As far as floaties, I was very happy with the puddle jumper arm floats we bought for Layla. It held her up really well and made her comfortable in the water. Most times she didn't even want us to hang onto her. We should have bought a set for Mariam. With her we used a speedo floatie and it just didn't work with keeping her balanced in the water. It floated fine but it would quickly flip her over. One other thing I highly recommend for taking little ones to the beach and bay are water shoes. You can find them for really cheap at Walmart.
I was also pretty diligent about wearing my sunhat and keeping my sunglasses on--hence why I ended up with my face much lighter than the rest of my body.
I also thought it would be fun to bring our collection of Ella+Mila nail polishes and we all had fun painting our nails one day. I wore the color "pool party". Oh, one thing that I wasn't crazy about that happened is my hair turned super brassy. I didn't even wet it that often, but just washing it daily and exposing it to the sun so long really did a number on it. I plan on buying some toner next week and seeing if I can fix it. I'll do a post about it if it comes out successfully.
Have a great weekend!