If you want to cover part of Bodmin moor with kids, I would highly recommend heading for Minnions in the south-east of the moor. There are several good circular walks here across moorland and take in a few things to spark the kids curiousity, taking you past the cheesering (natural stone outcrop in a balancing act), ruins of tin and silver mine engine houses and the hurlers (stone circles, said to be the petrifide participants of a hurling game who god turned to stone for playing on a sunday). At Minions there is also a tourist info centre. Another place which is a must with children is Landsend, this has some breath taking walks along the cliffs added with a leasure park. Kids also always seem captivated by being at the end of a country.
As for camping, in the Summer there is always a campsite near-by that can squeeze you in. But if you prefer the basic camping, head for a pub, inside you will find a farmer (or someone who knows one) they will usually be happy to find you a spot.