Sea World San Antonio - Allen,TX

I have never been to Sea World with my now 4 yr old son. But when he was 2 and 3, he just LOVED the Kiddie Park. http://kiddiepark.com/ If she likes carnival-type rides, I would recommend the "Unlimited Ride Band" which is cheaper on Wednesdays. Take a picnic and sit in the shaded picnic tables. You'll spend just the $13 for a few hours of exciting fun for her. (Yes it's outdoors, very small, but lots of shade trees).

There is a children's museum in downtown San Antonio. Nice but hard to find parking. sakids.org.
The Witte museum has a children's area. wittemuseum.org.
There's the zoo(but would probably be redundant if you're going to seaworld).

We went over Memorial weekend with our then 16 month old. We stayed at the Hilton which is minutes from SeaWorld. It's a very family friendly hotel (three pools; each night they lit fire pits for smores, turned on a big screen outdoor movie, opened a hamburger/hot dog near the movie/fire pits, etc.) with a package including stay, SeaWorld tickets and free shuttle to/from SeaWorld. It was pricey so there are plenty of other nearby options (Hyatt (also pricey), Holiday Inn, etc.). Check the online reviews because some of the hotels don't get good ratings. For instance, the Hilton was nice but not up to the standards of Hilton (hence arguably not worth the money) in my opinion.

We did SeaWorld over two partial days so there was no rush. They have opened a new water park but I am not sure it is age appropriate for a three year old. They do have a splashpad which is perfect for a three year old, though. We packed a wet bag in our stroller and spent time in both the park at the shows/feeding sea lions/roaming and also at the splashpad (there are changing rooms). I would recommend a stroller because it is a lot of walking. We did some of the shows - Shamu was average, Azul was eye catching and Cannery Row was cute fun.

In addition we went to the zoo because we are zoo people and it's a thing of ours. We also did the sunken gardens which are near the zoo. It was free and a quick roam around was do-able with a small child. It was for us but our son enjoyed the koi in the pond. We also hit up Splashtown because our son is a water nut. It was good family fun for the price in our opinion. They had several low entry wading pools with slides, water features, sprayers, etc. which is great for the little ones.

In the past we have also gone to the missions which are free admission (there are a total of 6 including the Alamo). El Mercado is interesting too as is the River Walk if you've never done it.

You will see a lot of young graduating Airman that just went through a grueling 8.5 weeks of training. Most of them will look like hell. I went there when I graduated, we took out kids. It was horrible to me because I couldn't do anything I was just trapped in my new blue uniform! LOL I am sure you will have plenty of fun. My youngest was 2, she enjoyed the dolphin show. They also have acrobatic water skiers that do routines. I recall a bunch of magic shows too. Enjoy and safe travels!