Personally, I'd be tempted to head in the opposite direction once on the continent and go Belgium/Holland. Lots to see and do there, and with the benefit of people being more willing to speak English.
That's not to say that the French don't speak English, they just sometimes like to let you think they don't
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Hi there, I second saintjimmy and saftlad in their recommendation for Belgium and in particular De Lilse Bergen, its a fab site and would meet your needs. Big pitches in a forest setting, man made beach around the beautiful swimming lake, lots of sporting facilities and shops close by. Plenty for both your children to do.