We are taking a two week vacation in July to the Grand Tetons/Yellowstone area. We have three kids, 13,11 & 5. I'm not sure whether to stay at a state park or campground. I have visions of camping on a river right below the Tetons, but is this possible? We will be in a tent as the cabins are to expensive. Must have flush toilets and showers. Also, a little entertainment wouldn't be bad. Don't want the kids to get bored. Can anyone recommend a good campground?

Check out the Grand Tetons National Park website for the detailed descriptions of camp grounds. The most popular tent area is Jenny Lake. According to the official word, it fills early in the day -- like 8 AM. In my experience, it tended to be filled with rock climbers who often stayed up late singing and drinking. So that should be good entertainment for your children.
Other campgrounds tend to be RV havens, but tents can be set up. There are also sites in the Teton National Forest, but these are a little farther away from the main attractions.
I know of no state parks in the immdediate area.
But, to be blunt, if you are worried about the children being bored, perhaps camping is not the best idea. There are no cable TV outlets that I recall.
If you head north to Yellowstone, the first camping area you come to is Lewis Lake. In my experience, it is not good for tent camping because of mosquitoes, particularly if the breeze is off the lake toward you. It is something of a family joke -- tall tale variety -- but we pulled in there once with the intent to set up our tent after lunch. Well I didn't say much when three big ones took my sandwich, but after I had to hit them with a tent pole to make them put my son down, we decided to look elsewhere.

I always loved camping with my family when we were kids! Started at age 4 and I went with them until late teens. Tetons and Yellowstone are incredibly beautiful. Coulter Bay (Teton Natl Prk)campgroud is very nice. It has a section for the lined up motorhomes, but it also has plenty of other loops for tents. Lots of hiking for all abilities, you can rent a canoe, watch the wildlife, take a horseback ride. Visit the town of Jackson, take in a cuckwagon dinner (many to choose from) and fun entertainment. Ride the tram up at Teton Village to the top of the ski mountain. Awesome view! Zillions of photo ops, especially in the early summer when there are literally carpets of wildflowers. Yellowstone is too big for words. Facinating mudpots, geysers, buffalo, everything. Even some bike riding trails. Take warm clothes for night time, it still gets cold in the summer at night.

In the tetons, I think the best campground is jenny lake. This is on a lake right below the mountains. I recall that is has flush toilets. I think you need to drive to another campground in the park to showers. At least 2 years ago, it was 1st come, and this spot fills up early.

In yellowstone, the tent spots need to be reserved in advance. I would plan a trip that has you moving to a few different campgrounds within the yeloowstone, so you can cover the "loop" in an efficient manner. In yellowstone, there are buffer lands (eg nat's forrest) surrounding the park. You can camp in these areas. IMHO, you really want to be closer to the things that make the trip to yellowstone so great. You can only to this from inside the park.

We stayed at Coulter Village and enjoyed it, except that it cost $3.00 per person to take a shower there. A little pricey for a family of five. There was another campground closer to Yellowstone that looked nice from the road, anyway. It was called Flagg Ranch and was about two miles outside the south gate of Yellowstone. Phone number is (307)543-2861. The book says they have hot showers and flush toilets. Your kids will love Yellowstone. All the entertainment you need is there. Our kids threw snowballs atop the Continental Divide, climbed rocks, and spent hours watching the geysers. The Grand Canyon of Yellowstone is spectacular but wear comfortable shoes. The trails are longer than they look. Have a good time.