You can do Centre Parcs on the cheap, or you can spend a small fortune...
I recently took ds for a weekend off peak at Elvedon Forest for £279 for a 2 bedroom executive lodge with maid service, towels, dishwasher etc included. You would not get that price in the school holidays though. There was only the 2 of us but if 4 people were sharing that would be £70 each for a weekend.
We are going at easter for a midweek and it's costing quite a bit more, even we're sharing with friends to help bring the cost down. So a 3 bed villa is coming out as £163 per person (although that does include an extra night as its midweek not weekend).
BUT we could pay a lot more than that if we went for the same executive villa.
The easter price includes extra cost for a central location and maid service too. And we only booked it recently.
We bring our own food and eat in mostly which keeps costs dowb. We also choose the activities we will pay extra for carefully. You can go totally overboard eating out and booking so much extra stuff that you don't get to spend much time in the pool or cycling about the village.
What's the appeal? It's near by (less than 2 hours drive) with no airports to negotiate, no parking costs no delayed flights.
And we get to really relax by doing activities together, chilling out together as well as being active. The nature is right on your door step with squirrels running across the roof and ducks on the patio waiting to be fed.
Basically we find it fun, and really get to spend time together as a family while leaving the stress or work etc behind.
It's magical being woken up by ducks quacking outside your bedroom window hoping for some bread and having a deer run right past as the childrn feed the geese and watching the squirrels run up and down the trees (and in your lodge given half a chance).
We wear ourselves out cycling, swimming and doing various activities, and we sleep soundly having had a really busy day doing things we enjoy.
We love it, but if it's not your thing then you may not ever get it.
So go and try it, but don't ever pay top whack when you do!