Road Trip to Texas

As others have said go to Fort Worth. But not for the ZOO. Come for the Texas experience. Go to the Stockyards and watch the Cattle drive. Have some Texas BBQ. Way differant than KC que. Take the kids to Six Flags and Wet N Wild. Definately drive around downtown Dallas and Fort Worth at night. The flavor of each city is so unique and worth seeing at night. My kids love it.
If you are going to only go to 1 zoo go to the San Antonio Zoo. It's 2nd in the nation, behind San Diego. It's amazing. There's a full size carousel out front and the SUnken Gardens are right next door (free and gorgeous). You can take a boat and train ride through the zoo. They have a great research facility you can peek into.
Between Fort Worth and San Antonio you will pass through Austin - 6th street all the way!! Go see the bridge under the police satation. There are thousands of bats that all ascend at dusk. Kids go nuts for that!
You will also pass through Fossil Rim Canyon. There is a Wildllife Ranch safari drive through.

We went to San Antonio last year for spring break and my kids actually asked if we could LIVE there, they loved it so much! You will love the people of SA, very warm and friendly and the city itself is beautiful.

Lots of good advice so far- just wanted to throw in that St. Patrick's day in SA is a ton of fun. Go down to the Riverwalk, they have a parade of "floats" that float on the water and they dye the water green. Our kids thought that was awesome. Check the times for it and get there early so you can get a good seat, it's crowded.

Our kids also liked the Alamo. It's also right downtown, too, and it's free. Seaworld was beyond amazing, very expensive, but oh so worth it. When we were there, the water park was not open yet and neither was Schilterbahn, not that it matters since we have one here now.

Unfortunately, I can't offer much about what to do on the way- we wanted to get to our destination right away... Have a safe trip and a good time there! It's a great spring break trip!

Waco has the Dr Pepper museum right off I35. Buda-right by Austin has huge Cabela's sporting goods with live fish and excellent displays. Texas State History Museum in Austin-about 5 blks off !35-4D show that is great.
In SA, Hyatt Hill Country Resort is extremely kid friendly, a little pricey but all your entertainment is there-tube floating, outdoor movies, beach area, s'mores at night, bikes and trails. The riverwalk hotels are high-check out Embassy Suites by the airport-beautiful place with indoor pool, cook to order breakfast and nightly managers reception. Straight shot down Hwy 281 to downtown. About 10 minutes. YOu can park in Rivercenter mall garage easily-around $10 daily.
The Alamo is free and w/in walking from the garage, Rainforest Cafe, ride the boats-they opened a new part of the Riverwalk last year. Walk to the tower-they have it totally pedestrian friendly-long walk connects to Hemisphere Plaza which has a nice wooden playground. Magik Children's Theatre is right next door-hilarious kid friendly plays. The Tower also has a 4d movie about SA that is worth seeing and the top of the Tower.
San Marcos has lots of neat places and don't forget Schlitterbahn.
I don't recommend SeaWorld or Fiesta since it is so stinking hot!!!

I am a little biased, but if you have kiddos, by pass Dallas and instead swing by Fort Worth and go to their zoo (ranked top 5 in the nation, if I am not mistaken). and watch the cattle drive in the Stockyards and eat some risky's barbque or enjoy live music at the White Elephant!!
FYI: the chisohlm trail ran through the stockyards up to Kansas and could be a fun tie for the trip!!
In San Antonio there is Sea World, the river walk and the alamo!! So much fun.
Austin has the state capitol and two places featured on ManVs. Food (if you like that sort of thing - my family does - LOL!) Driftwood barbeque and a little place called Juan in a million (or maybe that is what the big breakfast burrito is called) but they are known for breakfast. . .
Hope this helps a little. I am sure you will get a lot of great suggestions!

Not sure how old your kids are, but if you go through Fort Worth instead of dallas, you could do the zoo. Its an awesome zoo, I think ranked in the top 10 in the nation. There is the stockyards as well. Good museums also, and the kids museum is pretty cool too. Botanical gardens are always nice to visit as well. There's a great restaurant called Joe T's that serves good mexican food and really good margaritas and its close to the stockyards. So you could visit the stockyards in the afternoon and follow up with dinner at Joe T's after. Also worth checking out is the city of grapevine's website. they are always doing some sort of festival in the summer. its a little north of fort worth. they have wineries you could tour if that's somethign you are interested in.

Like others have mentioned, the Ft. Worth Stockyards are so much fun. You will feel like you've gone back in time to the old west! The Ft. Worth zoo is ranked in the top 10, but the San Antonio zoo is number 2. Both are wonderful! Joe T Garcia's is a fabulous mexican restaurant that has a gorgeous patio. It's not too far from the Stockyards. Sundance Square in Ft. Worth has tons of things to do as well. I definitely prefer Ft. Worth to Dallas. Have a wonderful vacation!

I live in Dallas/Ft. Worth area. The Dallas World Aquarium is fantastic and, also, the Ft. Worth Zoo. Both cities have wonderful children's museum, also. Austin has the state capitol and a nice children's museum. You should, also, take a swim in Barton Springs and play at the park next door-Zilker Park. San Antonio has a great zoo, the Riverwalk, the Alamo and, of course, Sea World and Fiesta Texas. We have stayed at the Hyatt Hill Country Resort near Sea World and I highly recommend it!! I can't help but mention some of the fabulous restaurants along the way, too.
Ft. Worth-Joe T Garcia's
Austin-Magnolia Cafe for breakfast and Guerros for tacos
San Antonio-I have eaten at Casa Rio on the Riverwalk every trip to SA since I was a child

toby kieths bar and grill and the science place right by the zoo in okc cant remeber the name but if you look up the okc zoo it is on the same road before you get to the zoo

In San Antonio Sea World is loads of fun for the kids. Six Flags if they are a bit older. In New Braunfels (just north of San Antonio on I-35) there is Schlitterbahn, which is a HUGE waterpark - VERY family friendly - great for all ages (we go there at least 6 times a summer, and I have a 2 and 4 year old). They also have the McKenna Children's Museum, which is by far the best children's museum I have ever been to.
Send me a private message if you have any more San Antonio specific questions. It is a great place for a family vacation!

Stop at The Salt Lick BBQ in Driftwood, just outside of Austin. This BYOB joint has great ribs and the kids will love the food! While in San Antonio and if you're going to check out downtown, stop by Hemisfair Park where they have a large playground and plenty of shaded seating to relax. You can check out the water fountain near the Henry B. Gonzalez Convention Center and maybe catch a kids play at the Magik Theatre.

Ft. Worth zoo near Dallas is a must do. .
Also, near San antonio is a natural bridge caverns and drive through wildlife zoo. The animals come up to the car and you can feed them. It is maybe 45 minutes from Sea World.
Sea World is a must and we swam with the belugas(expensive, but worth it).

Coming from OKC, if you like to camp, Turner Falls is usually a fun stop. You go swimming in the water falls. The Dallas Museum of Nature & science is usually a great family place to hit up. It's very hands on, fun for everyone. The dino dig is inside, which is nice when it's 100 degrees outside. The Fort Worth Zoo is a wonderful zoo. The Fort Worth Stockyards can be fun too. There are restaurants, the cattle maze, the cattle drive and a mechanical bull. In Austin, if you are there in the evening, check out the bats at Congress Street bridge.Town Lake in Austin is fun if you like outdoor activities...boating, biking, hiking. Down town Austin has lots of fun restaurants and quirky shops that are fun to browse. In San Antonio, we usually stay near the River Walk. It's a touristy thing to do. Kids usually enjoy it. THe Alamo is nearby. Sea World is fantastic. Right now a day pass is the same cost as a season pass, so you can split up that visit. San Antonio also has a Six Flags.