Sun? just keep re applying sunscreen...no matter how water proof...My daughter is dark skinned, but as a baby the skin is more sensitive to the sun unless they've been exposed in small doses (like a warm climate resident).
Make him wear a hat!! The sun reflects into those tiny eyes. You don't want to slather the lotion right onto the eye lids. The hat protects the scalp too....if he is blonde or has thin hair....lotion the head. Even the part in the hair will burn.
I had a pop up style hut....like a play hut....we cut the sides so there was only a roof and the sides tied back. My daughter played in it with the sides down (but she was like 7-8 months). and we tied the sides back and put it over the pack and play when she napped on the beach so she got a nice breeze in the shade.
Change his clothes before napping....the sand will irritate and cause rashes....even if he falls asleep, change him in his sleep if you have to.
Be careful in the ocean that young, they want to crawl towards the waves and it takes only one big waves to give them a gulp of water.
Fresh water runs the risk of severe respiratory infection....
Oceans also run the risk of pulmonary edema when inhaled....
Pool water can not be trusted...
Is it a reputable hotel pool or park?
Some cheezy hotels have terrible pool maintenance.
If the pool area looks dirty, don't take the risk with the baby.
Reputable parks and hotels have high tech equipment and not just some after school kids running water tests once a week.