Lunch and a Hayride at Cox Farms, Centreville Virginia 

We went on a Monday so some of the food vendors were closed. It was a discount day at $10 per person.
Cost for meals is reasonable for this area, there are plenty of activities for children up to perhaps 10 years of age. After that, the evening activities, Fields of Fear is apt to be more appealing for teens. However, even for teenagers, a day at Cox Farms is quite fun, with the Corn Maze and the Hayride being the most fun for older kids.
There is also a petting zoo!