I think the only site you'll find open at that time is La Croix du Vieux Pont, which is near Soissons. However, they do run a daily (??? in low season it may be less frequent) trip to Disneyland Paris, or you can get a train from any of the nearby stations.
It is open all year, and has permanent holiday homes, and also plenty of accommodation to let, so there should be plenty of other people around whatever time of year you plan to stay there.