We went for the first time this year (not Whinfell though) and absolutely loved it (with similar aged children). We were in our school hols which are different to most other areas, so not officially school hols according to Center Parcs, but it was still pretty rammed in the pool area during the day. If you're going in October half term, be prepared for it to be busy. If your children like doing the slides / rapids etc there will probably be big queues, so my top advice would be to switch your day around so that you use the pool from about tea time to when it closes. Most of the families with pre-school children / babies had gone by that time and there were few queues and it was pretty much perfect. There was a part of the pool area called Treasure Cove (for little ones but I have a 5yr old too) and we had that completely to ourselves one night. I think it closed at 9pm so we used to go from say 6pm-9pm. It used to be all lit up at night too - they loved it. Children would be in bed at 9.45- 10pm (late for my children) but slept in until 9am (unheard of) so we all got a break
.
We did quite a lot of what I would say are the cheaper activities - roller skating, French boules, short tennis (which was great), the Dad and Lads football tournament, and the katakanu on the lake. We only booked one of those beforehand, there was plenty of availability.
The lodge was lovely, agree with a couple of DVDs, 2 lots of swimming kit, dishwasher tablets, we found the on-site shop wasn't massively expensive but it was quite limited. The bakery was great though. We ate out a couple of times (Café Rouge was lovely). Every lodge had barbecue equipment so depending on the weather you could barbecue. If you're eating in, kitchen perfectly well equipped.
And bikes - this is what made it I think for us, it meant it was easy peasy to go back to the lodge for lunch / a drink etc, and the kids actually loved bike riding. You can hire the chunky D locks from the bike store when you get there (for free - you have to pay £15 but you get that back when you hand the lock back in).