The table tennis, soft tennis and outdoor bowling are all really good value - especially if you book at an unpopular time - e.g. earlier in the morning or dinner time. We've beento Whinfell about 9 times since boys were babies up to teenagers.
All good tips re the early arrival and swimming etc. I've never really thought the shop was that bad compared to normal - they have a hot counter that does pies and sausage rolls which can be a great after swim lunch treat.
It's also worth seeking out the pond if you have bikes (it's to the South East of the park) not sure what wildlife there will be, but we alwasy took buckets and nets and have got spawn, tadpole, dragon flies etc at various times......and it's free.
I think it definitely worls out cheaper when the kids are youngert and happy enough with the play parks, swimming pool and general cycling about - it gets expensive when you have teens as the eat full adult meals and have done all the cheap activities!
I think hiring a canoe/pedalo is fairly reasonable if the water activities are still open.
We also take meals for some nights. I usually freeze some bolognaise and then take it with us - it's usually just defrosted by the time you get settled in and ready for a meal. Then I would either go out for an ice-cream or pancake or cake from the shop as a holiday treat.
Hope you have a fab time.
Just for those who said it's cheaper to go in the Scottish holidays - it's not cheaper at Whinfell as it's the closest to Scotland and they are usually well aware of when the main holidays are. We have occasionally picked up a bargain when we've had local in service days. Otherwise, if you want a bargain then you need to drive to one of the ones in the South.