We took our two kids, ages ten and thirteen, to Claytons for dinner one night during our week in South Padre Island. The boys had burgers, which were tasty. My ceviche was excellent -- I'd highly recommend it if you are a fan. All of the beer is sold by the can. Prices were pretty reasonable considering you are eating right on the sand on the ocean.
You can eat either outdoors under full sun (or stars) or under the canopy. During the day, you have beautiful ocean views. At night, it can be chilly, so bring a sweatshirt or jacket.
We were at Clayton's the week after Texas Week, so it was not too busy. There were a few spring break college-age kids from out-of-state, and several families with kids. During spring break, the place is a madhouse filled with inebriated 19-year-olds, so unless you're a college student, steer clear during that time in March!