If you decide to visit Port Aransas, you'll pass through San Antonio on I35 where you can visit the Alamo and the kids might also enjoy the zoo, as well as the River Walk. There is also Fiesta Texas, a theme park, and Sea World. The closest RV parks to the downtown area (Alamo is downtown and zoo is just north of downtown) are the KOA and Traveler's World. You could easily visit the Alamo and zoo in one day. Fiesta Texas and Sea World are northwest and west respectively, of the city, and not as convenient to your route should you decide to go to Port Aransas. Hope you enjoy your visit, wherever you decide to go!