J.W.
There is a great place just north of Lewisville on the lake. It's called Hickory Creek. Once at the campsite, you feel like your hours away, but very close to I35 to get home quickly if you need.
There is also a WalMart within a 5 minute drive. Campsites 52 and 54 are directly across from the playground, so you can watch the kids from your site. All the sites in that area have great lake views and access if they want to swim or put their feet in.
There are hiking trails and woods to go exploring, and a boat dock to go fishing down the road in another area. In the sites where I've suggested (52 and 54), each site has electricity and water if you need.
I think this is a great place, especially for first time families due to the proximity, facilities and nearby shopping, etc.
We've had great fun out there with friends/family and have had kids out there from ages 3 to 12 and everyone has fun! ENJOY!!
http://www.recreation.gov/camping/map_of_Hickory_Creek_Tx...