I second Isle Du Bois. Don't go on the other side of Ray Roberts further north. We didn't like it at all.
Be careful when you pick an area and make sure it has the bathrooms you want if you need to go in the middle of the night nearby. The primitive sites are lucky to have porta potties nearby and you will have to walk your stuff to the site. IMO, not a lot of fun with 2 youngsters. Believe me, that is a voice of experience talking. I had the 2y/o there twice. It was very pretty though. It had a lot of privacy so if the kiddos weren't having a good time it wouldn't bother a lot of people.
My first pick is actually Hickory Creek park just north of Lewisville for a first time. It isn't far away but they have a beach, several sites near flushing toilets, a playground, and trails and places to ride bikes. You can pull your car right next to the site which makes clean up and unloading much easier. The people have always been very friendly. We chose a site right across the "drive" from the bathrooms. It was far away enought that you didn't hear noise but close enough that you weren't dreading having to get up at night or 6 times while you are trying to cook dinner.
Remember to keep it simple in every way. The kiddos will have fun just getting to run around, pick up sticks, and just be outside. It is amazing how many fresh vegetables and fruit they will eat when it is just sitting out there for them to help themselves. It is so much fun to be able to give them more independence b/c it is alright to make a mess.
Get bright lanterns and consider "head" lamps for everyone. We got those for Cmas and it was a lifesaver. Much easier to get jammies on and make potty runs when your hands were free. I found $10 ones at Home Depot of all places at Cmas time.
Oh, the other thing we learned was depending on how you wanted to handle bedtimes, you may need to go to sleep with the kiddos. Our littlest at 2y/o wouldn't stop crying and go to sleep in the tent. She was the last to sleep even once we went in there. I was really looking forward to Mommy and Daddy time by the fire. This last time as a 3y/o she conked out with a lantern on low inside the tent. It may have been the fact that it was 10:30 at night too. : )
Anyway, after my novel..... if you want to chat more feel free to PM me and we can talk more.