I sent these photos to a local bird expert who is an ebird reviewer for our area. He confirmed this seemed to be a family group. He also felt they did indeed nest nearby. Over the past decade he had been involved in a long term project to establish a breeding colony which began in SouthSide in Dallas, then moved from there to Hagerman in good numbers. The young ones stayed with the parents into August. Very cool to see them show up at White Rock with young now.
Interior Least Tern (Sternula antillarum ssp. athalassos)