Summer trip - 2 kids under 10

Go to Colorado and hit the mountains

"under 10" is a pretty wide range. If they are 5-6 or older I would head west to colorado. Easy to get there and its hard not to enjoy it. We really like southwest CO (Telluride, Durango, Ouray) and have done it a couple of times with the kids. Western north carolina is another option. Easy drive from LA and plenty to do.

both would be great spots, I'd lean Estes for the experience and to avoid the heat. New Braunfels/San Antonio would be more enjoyable in the spring or fall IMO.

As a few others have said, Pigeon Forge/Gatlinburg area is great for kids. There is lots of things to do around there. Rent a cabin in the mountains, Dollywood is the nicest, cleanest amusement park I've ever been to and the food there is good as well. You can rent side-by-side ATV's and drive them on the road, take an ATV trip to Cades Cove in Smokey Mountain National Park and look for bears, we saw about 10 of them pretty close. There is an aquarium in Gatlinburg, Dinner shows in Pigeon Forge are a good time and kids that age will like them. There is a place called Anakeesta that the kids will like, mountain coasters, a suspension bridge between 2 mountain peaks with a glass bottom in the middle, ATV mountain tour was fun. There is plenty of things there to keep you busy for a trip, of course there is the largest Buckey's in the world in Sevierville that's on the way. I'd think you'd have a good time.

Branson is similar to Pigeon Forge, it's just doesn't have the scenery like the Smokey Mountains, there is Silver Dollar City amusement park there as well.

Hot Springs is a cool little place in Arkansas, If you like the lake there are several around there that are nice, Lake Hamilton is in Hot Springs, Lake Catherine, Lake DeGray, Lake Ouachita. You can try and rent a houseboat, but they sell out quick, so you better get on the ball if you want to go that route.

San Antonio/ New Braunfels is fun as well, big city with big city things to do, Schlitterbahn water park is awesome. There are 2 separate locations there, one is the original park where the water is taken out of the comal river, its cold but fun, the other one is right down the road, we spent 1 day at the old park and 1 at the newer one.

Personally, with kids that age, Pigeon Forge/Gatlinburg area would be your best bet. Estes Park is a beautiful place, but your kids won't really care about the scenery yet, they want to be entertained, and I don't know if you'd want your less than 10-year-olds on a horse back trail ride but maybe your kids are different than mine which is quite possible. Anyway, wherever you go, enjoy your trip.