Are you looking for award space like your other post says? If so, then you will be driven by availability - if any.

Also, even IF you could find availability, I think it would be pushing it to try and see a city in a couple of hours. Remember, you need to deplane, exit the airport, get transportation to the city, get back to the airport, go through security etc. You will probably have a couple of hours at most to see the sites - not something I would want to do with a 2 year old and an 8 year old.