My family of 4 (includes two young adults) will have about 6-7 hours on a layover in August during the late morning and afternoon. We thought we would go to Charlotte for lunch and to walk around. Is there someplace particular we should go or just head for downtown

You could go downtown to the Bechtler Museum, have lunch at the Mint (or the Bechtler), then go to the Mint Museum. Two VERY fine experiences.
Then down the street a way is the Levine Museum of the New South, also an excellent experience.

You could go to SouthPark and have a great lunch and good shopping.
YOu could go to SouthEnd and have lunch and a slightly different kind of shopping.

If you're at all interested in motorsports, the new Nascar Museum downtown would be great. (My niece's family aren't big fans, but still greatly enjoyed it & were impressed). We also found a restaurant named Harry & Jeans that had good food, if you happen to be in the downtown area.

thank you

Sadly Harry and Jeans closed uptown a couple of years ago (I liked it too). Plenty of other restaurants and things to do downtown (we call it uptown) for a few hours.

any good restaurants you can recommend for lunch in downtown (uptown) area. Salads and sandwiches are fine.

One of our favorites (http://www.cocoosteria.com/) is Italian but has a long list of salads and panini for lunch. Not sure why the website indicates they're not open for lunch on Fridays - they are.

Next door, Rira's is fun and usually good - http://www.rira.com/rira/charlotte.html

Across the street is a good farm to table choice - Harvest Moon Grille - http://harvestmoongrillecharlotte.com/menu/

A bit further down Tryon is Rock Bottom Brewery - typical brewery type fair - usually pretty good.

On the other end of downtown the restaurant in the new Mint Museum is very good but also a bit pricey - http://halcyonflavors.com/

There is also a more casual counter service option in the Bechler Museum next door.

If you go to the bechtler, the restaurant there has a good lunch--run by friends of ours, and written up positively when they opened. Probably not a huge selection.

Is there a train or bus that reuns from airport to downtown.

There is a bus:

http://charmeck.org/city/charlotte/c.../sprinter.aspx

But with 4 of you, I'd probably opt for the quicker cab ride.

If your layover is shorter, but long enough to see something there is a small air museum adjacent to the airport.

The air museum has the USairways flight that crashed into the Hudson en route to Charlotte--The Miracle on the Hudson plane--just an FYI. It is not "walking distance"--you'd need a cab.

AND it isn't open all the time. Don't know the hours.