J.C.
This heat is CRAZY! I have been here twelve years and never has it been this hot this early in the summer.
The free movies are on Tuesdays and Wednesdays. They have a pretty good schedule this year. You can see the schedule online or you can pick one up at the theater. I got a copy of it from Cielo Vista near Ingram.
The Witte Museum is free on Tuesday evenings.
All of the indoor play places have specials. I own Fiddlestiks (Culebra) and for the entire month of July it is only $5 for open play. There is Just Add Children (Mainland) and they are $5 for open play. There is Funtastic Playland and Dynamoze as well, but I am not sure of their specials.
Also, it is a good drive, but the McKenna Children's Museum is in New Braunfels and well worth the trip.
There are a few suggestions. I am sure you will gets tons of suggestions since we are ALL trying to find things to do with our kids to beat this heat this year. I am looking to hearing what other people have to say as well.