OK I've found a venue for next summer!
We went last night, and it was lovely: I think it would suit all ages. We had 6-18 yr-olds with us, and they all had a great time; and the adults too. Lakeland Maize Maze . There's a maze (obviously), but also trampolines, slide, ride-on tractors, picnic areas, shop, pedal go-karts (£1 per go), loads of animals (pigs, sheep, alpacas, etc.) It's at Sedgwick, which is very near Kendal; but at the roundabout where Ursula goes wrong you take a different turn!
Costs £4.50 for adults, £3.50 for children, and U3s free. £15 for family ticket. Discount for groups of 20+
We had a group booking, and used their gas barbecue and cooked our own food: It all worked really well.
There's also a campsite (fairly basic I think), if anyone fancies staying overnight!
What do you think?!