www.FORPWC.org is a family oriented off road club. They have property in Nokesville that is family friendly. As well as more advanced trails in Catlett and Dahlgren. There is a membership fee, but it covers all three riding areas. Or like 5-punks said, make a trip out to his place and blast around his yard one afternoon.
The cove is pretty rocky and wouldn't be good for first time kids.
And this weekend, the club is hosting a open ride day at the 301 (Dahlgren) property on Sunday. It's a more advanced single track trail, no quads, about 10 miles long.