Wild camping is not as fun as it sounds for the kids, it can be done in Snowdonia I have done it loads of times but best to pitch late at night and pack up early. And I would definatley not have a camp fire, small camping stove only. Ive never had any problem.
If you want to check out this web site Click here
it lists camp sites that allow campfires, and some are just fields which allow camping.