in order of distance from Baz:
Langdon Hills – theres miles of it if you can find it all.
vistors centre here can’t remember if they charge to park http://binged.it/1kJaFrh but you can park for free here
http://binged.it/1kJbn7R outside unit 3 because i wont mind and you can ride completely offroad from there to the park
thorndon south is probably best if your family have ‘mountain’ bikes ahem as mentioned by khani it’s hardpacked and you can’t get lost and there is a cafe halfway round and at the end and loos and everything. they rob you a couple of quid for parking though. There is parking at the other end near the second cafe but it’s a little bit further to drive. if south is full try the north one – but instead of parking where everyone else does carry on past the first carpark for about 1/3 of a miles and there is a huge carpark where the horseboxes park and it is generally empty.
epping – park at the tea hut here now they have sorted the car park out there is always tons of space
http://binged.it/1kJczIs
public toilet across the way in the pub carpark. there is miles and miles of it but also hard packed stuff too and also another tea hut here. http://binged.it/1lVFeg9 which if you follow the track on the map gets you there, nothing scary but there might be some pushing.