Hi Angie,
We go in February every year to Whinfell or Sherwood Forest and each has it's good and bad points. Reasonable cost in Feb., very expensive at most other times.
Most families use the Tropical Swimming centre as a main venue which is great, (paradise for kids of all ages), but there are numerous other sporting activities both indoor and outdoor. The accomodation units are fully self-contained, and we take frozen meals for each evening's dinner to cut the cost. Eating out and drinks are very expensive, but self catering is very easy. The on site supermarket is the only place where prices seem about normal.
If you go, arrive early on the first day, (10amish), because although you can't get to your accommodation until 2pm you can go straight into the pool area until then. Similarly on your last day, use the pool on leaving your villa and you can leave the complex as late as you like. It gives you another full day.
We've tried Mon. to Mon., but Mon to Friday is better if you make full use of your time.
It's certainly worth trying it at least once, if only for the experience.
By the way, don't expect anything other than bog standard British service.
HTH,
Bill.