Stinky's for lunch for a 3.5 yo or for someone 20 times that age is great.
Last trip dinner with a 3.5 yo? You know, one 3.5 yo is different than a bunch of kids. As much as kids make me nervous and make me feel out of control, I can handle one. We only had one child (wanted more, but not so lucky). We always assigned one of us as a "designated martyr" who left the table with her if it appeared that she was bothering others. By the time she was five, she had been to the best restaurants in Paris, Rome, London, Amsterdam, Luzern, Bermuda, NYC, ATL, and many five-star resorts in the US.
You're at the beach. Everything is casual. Just go where you want to go. It will be a learning experience for your child. Just make sure that you have a designated martyr. LOL.