Recently traveled to San Juan area (Feb. 2015). I often look to Chowhound for recommendations when we travel. We are a family of five (kids ages 7-13) and we had my 70 year old mother with us. We received a list of restaurants from a friend who lives in San Juan. His recommendations were great - places with delicious food and good atmosphere.
La Casita de Miramar (on Ave. Miramar in Condado area) - the 6 of us ate on the patio (great atmosphere although started to get a little buggy). Fish dishes were delicious, server Alejandro was very helpful and friendly, and best sangria we had on the island. Enough options for our kids. They take reservations.
La Cueva del Mar (in Old San Juan) - good seafood and service. Nice place to stop when we were walking around old San Juan. options for kids.
My husband and I went to the three places below at 7pm or later (without the kids and my mother). They are all close together in the Condado area. Our kids are used to eating out and are well behaved, but I was glad they weren't with us. It's more of a grown up crowd in the evenings.
El Pescador - Very fresh fish. Tiny place (not fancy) and be prepared to wait. I doubt they take reservations.
Santaella - great atmosphere and nice selection of food.
Jose Enrique - this was our best meal of the trip. We had grouper and mahi mahi and it was outstanding. Coconut mousse dessert is still in my dreams...
Marmalade - we didn't make it here, but would love to try it next time.