They are doing this all through February for 4-12 year olds. I took my DS1(5) last year and he LOVED it. It's just sliding down a slope in a big rubber ring thing but my Ds thought it was the most fun ever. It was £4 something for half an hour. He was shattered after it so 30 minutes was just spot on.
Just thought i'd post about it here for anyone with kids in that age group. Something different to soft play.