We've used Keycamp many times and can;t rate them highly enough
Well kept, clean sites and the brochures describe them just as they are
Vacansoeil, though, are better VFM - or they were last time I looked. However, once you travel with KC or Eurocamp you then become eligible for a loyalty discount if you use them again
We love Berny Riviere - you can also book direct with this site for a cheaper option but then you will have to pay for your own ferry crossing so it's swings and roundabouts
You get money off when sailing from somewhere other than Dover (mind you it's only about 3 hours from Dover to Poole so you could manage it ). Berny Riviere is a further 3 hour drive from Calais
My absolutel favourite sitge in France is here
http://www.caravancampingsites.co.uk/france/77 /courtillesdulido.htm
Very quiet, enclosed and ideal for children to run around. Beautiful site as well, near a train station although you can;t really hear the trains and near the Seine. Also lots ot do in the surrounding area - about a 3 hour drive form Calais
Should you choose Berny Riviere give me a shout - I have a shed load of information for you