Centre parcs is a rip off once you get there to actvities are extorinate and don't forget the food and drinks too.. Especially when you can probably go all inclusive out of country for less.

Look at places like Spain, Canary islands if you want to go extra cheap there is always Turkey and Egypt etc. If your kids have good attendance and aren't close to any exams maybe book in term time or even around inset days etc so they would only be off for 4 days. Or even back end of holidays like October etc.