Our family has just started camping and been to a couple of sites:
Fron Farm http://www.fronfarmcaravanpark.co.uk/
Nice place, great for kids. Just outside Mold so not far to go.
Near Caernarfon, pebble beach nearby which the kids loved, great view of Snowdon and a good spot for exploring North West Wales
Been using a mixture of TripAdvisor and http://www.ukcampsite.co.uk
to narrow down the search. The reviews seem reasonably accurate once a few are on there and ukcampsite is particularly good for checking for facilities (electric hook up is an essential for us for example).
Thanks for sharing those links Garygadge, might be trying Manorafon soon.