Honestly. I spent a lot of time in that area. With that age group look into Schlitterbahn. It is the world's biggest water park and is a lot of fun. That area (New Braunfels) is good for shopping too, with a very large outlet also nearby.
IN SA, there is a Six Flags with a free waterpark (used to be free, been a while it started as an independant, like Jazzland)
I enjoy the riverwalk, but have never had a good meal there. My go to is always La Margarita near the mercado.
Spend a day at Guadaloupe State Park and Overlook Park at the dam at Canyon Lake then ride down river road (Guadaloupe River). Beautiful country. Natural Bridge Caverns is nice for the kids also. Plenty of outdoorsy things to do north of town