Riding in northern France?

Anybody done much riding in northern France, can find a bit online listing VTT routes but do they have anything equivalent to trail centres? Thinking about places to ride when I go away with the mrs and the little one, taking the caravan down to the alps is a no no for the next few years, the drive would be not a great deal of fun with a toddler. I have driven to morzine quite a few times for snowboarding trips so know what the journey is like.

I hear the grading of routes in France is based more on distance than technical difficulty, failing places in France Germany or Belgium could also work.