Hi there,
There are two Dutch and two Belgian Center Parcs reasonably close to the tunnel - Port Zelande and De Kempervennen in the Netherlands and De Vossemeren and Erperheide in Belgium. The Center Parcs website has a decent map - so you can see exactly where they are.
None of the Take the Family team have personally visited these four villages to date, but all receive reasonable to good reviews. All are significantly less expensive than the British villages with accommodation a little more basic. Let us know how you get on! If anyone viewing this thread has visited one of these four Parcs what are they like?