The best advice I ever received regarding what to do with babies at the beach, was take a paddle pool (Blow-up kind works best if you don't have any place to store the hard plastic kind) and a beach umbrella. My husband would go ahead of the rest of us and set up our chairs and the pool with the umbrella situated so that the pool would be shaded for hours. Yes, they can still get into the sand, but we always would take them down to the water to rinse off and play a little. When we would come back up to the pool and chairs, they were usually ready for a nap, so in goes the blanket for a bed. So, DON'T add water to the pool. We made that mistake the first time we used the pool/umbrella.
Hope this works for you.