We went up to Turner Falls in Oklahoma last summer for the day. They have a big waterfall, plus lots of little falls. We swam, went hiking in steep rocky areas looking for caves (found some), and played in the falls area. You could jump off a small cliff into a waterhole area that also had slides and diving boards. The kids did great.Last year, they were 4 and 6. My daughter was an excellent climber and my son had no fear of the HIGH, fast slide into the water hole. We also took a side trip to a drive through animal area where the animals came up to the car and you could feed them. Needless to say, I screamed a couple times when they stuck their heads in my window with their mouths open. I do NOT like zebras and emus- they tried to eat me!Of course my kids loved that and still talk about how funny it was to this day.Looking back on it- it was pretty funny and I wasn't really being eaten- but I'm a chicken at times! ;) The kids werent' scared at all. The deer, donkeys, horses, and giraffes were nice. I thought the buffalo was going to ram my husbands car! It didn't - just gave us a stare down. It was actually REALLY fun. I'm not sure which part I liked the best. The views from our hike were beautiful. :) It was a great last trip of the summer. Plus, it was short- we were gone for the day.
Now, my parents live in New Braunfels and heading down there/San Antonio is always great. A lot of people head to schlitterbaun in NB, but with little kids I think it's too expensive. Once they get older= it's more worth it. I know we'll have season passes in a couple years. Anyway, there is another place that's GREAT for kids your age and I take mine all the time when we go to my moms. Go to Landa Park. There's a great park with paddle boats, picnic tables, ponds, streams, a train they can ride around the park ($2 and worth it), plus some great playground equipment. Also, they have a waterpark area there that has the natural river water, swimming area, zip line, climbing stuff, and slides. It's small- but only like $4 or so. We usually play in the park in the morning, picnic lunch, and then go to the water area. NOt sure which days, but I know some don't open til 10 or 12...
Also in NB, a great children's museum. I "think" it's called McKenna Children's Museum. It's not far from Landa Park. Your girls will not want to leave. I don't remember the price for a day, but it's worth it. They have different areas for the kids to play and explore- dramatic play. A hospital, astronaut area, house, bank, construction area, train area, camping area, art classes, sand/water play, and probably more. Eat before or after you go, there's not a place for that.
Of course, not 15 minutes from NB is San Marcos and the outlets- tons! :) I'm sure you already know a lot about San Antonio, but the riverwalk is so much fun. Sea world is a can't miss. We just got season passes to Fiesta Texas when we went down at Spring Break. You can use them at Six Flags over Texas too- so that's a good deal. Ok, gotta go take my daughter to school. I talked WAY more than I planned. :) Hope it helped. I'll be in NB and San Antonio a lot this summer so I can check on more for you if you need me too.