K.B.
You don't say the age of the kids, but there are lots of good places to go in Texas. Of course, San Antonio is one of the preferred vacation spots with Sea World and the Riverwalk, it makes a great family vacation. The Big Bend area is also wonderful if you want more of a nature experience. But if you don't want to drive too far and keep the cost down, I highly recommend the Glen Rose area. It is only one and a half hours or so from Dallas and has lots to offer. If you want something rustic, then Tres Rios is a great place for camping or renting a cabin. We have not been in several years, so I am not as up to date on the hotels. Years ago we stayed at the Best Western and it was wonderful. Lots of families and the owners were really trying to make it fun. They had free popcorn and other snacks every afternoon and even a cook out one evening.
Things to do in that area - Fossil Rim Animal Park, Dinosaur Valley State Park (also nice for camping) and Dinosaur World are the three main attractions.
If you go, look for Big Rocks park. It is a city park off the main drag that is just a bunch of huge rocks to climb on and a small beach area by a river (more of a creek at this location, not deep but perfect for wading). This was my kids favorite thing when they were young. Could spend all day there. Also, outside of town is a small little fossil store (if it is still there). I think it was called the Rock Shop or something like that. The man that ran it was very knowledgeable about fossils and told us where to go and how to hunt for fossils. There are lots of Bar-B-Q places in town, but ask about the place outside of town that is only open on the weekends. It is a lot of fun to take a family. It is on a family ranch in the middle of nowhere. While you wait for a table, families are playing football or frisbee on the large lawn.
You are also close to Granbury and there are several attractions there. We liked to take the kids to the Brazos Drive-In, a real old fashion drive-in theater. Both cities have neat little historic downtown areas to wander around. The Comanche Peak Nuclear Plant is nearby and has an interesting and educational information center.
Like I said, it has been several years since we have been, but we used to go almost once a year when our kids were under 12. Google Glen Rose and Granbury to see what all there is to do. Trip Advisor is also good for giving you info about vacation spots. If you go, be sure to ask the locals for tips, because most of them were very helpful and that is how we learned about the off the main drag type of things that ended up being our favorite!