When does the weather typically allow swimming in the area without kids thinking way to cold

Looking to go first weekend of March or April although March is better logistically I would think April gives better chance to do more beach/ water stuff

Lots of good information here including forecasts

https://www.seatemperature.org/north-america/united-states/port-aransas.htm

The water on the Texas Gulf Coast is typically cut up until late May or early June. It will be warm enough to swim in early May, but high tides and rip currents can be common.

The Texas Gulf is typically amazing in September and October.

Edit: the beat beach in Texas is SPI, but for some reason the water is always a bit colder there. Currents and a deep eddy are to blame.