Our younger two kids and I, aged four and nearly two, had a very nice Monday morning at the Land of Play in Manchester's Trafford Park. The place is very new, as of October 2009, and all the equipment is practically pristine. The unique selling point of Land of Play is the electric go-karts. Both kids loved them. The four-year-old was off on his own one and I could sit on the tail fin of the two-year-old's correcting the steering as subtly as possible. There was the standard climbing activity area, of medium size compared with the others of our acquaintance. The climbing was fine for the two and four-year-old, but would have been too easy for our seven-year-old.
The entrance fee was very reasonable. It was about £4.50 each after a 10% discount coupon that the Google Maps entry for the company offered me. The kart rides cost another £1 each, but you got a reasonable length go for the money. It has a cafe serving reasonably priced, if basic grub.
The main disappointment for me was that the environment didn't manage to shake off the feeling of industrial park. Sure it was clean, but there was only a passing attempt made at child-friendly decoration. That said I think we liked it enough to make another visit.