My two DSs 7 yo and 3yo really like Gambados, which is near is. There are several around the country. Lots of varied things to do including separate areas for 0-2 year olds, separate area for up to 3yos and a massive area for all ages. I like that there is a massive slide which four people can go down at the same time. I also like that I am not bent over double in the play frame and can stand up.
There is also a carousel and a dodgems. Mine don't like the carousel as it makes them feel sick, but they love the dodgems. Unfortunately, they imply have two cars which allow a child and adult to rode together, which is not enough.
It's pricey, if think it costs me £25 to take them both. But it's really good. Food is fab too, jacket potatoes, pizza and pasta dishes all freshly cooked to order. We usually spend at least £20 in the cafe when we are there. I don't like that they have machines which sell slush puppies, candy floss etc.
Kid space in Croydon is fantastic too. Their younger children bit is something incredible. Lots of sensory stuff, trampolines, but challenging play too.
Their wooden play frame for older children (it's the kind of place where you wear shoes as it is hard underfoot) is very challenging in parts and has great ball shooting, a climbing wall, air hockey etc.
Pricier than Gambados, but we only go maybe twice a year.
A good offer that Gambados do to get trade in the summer is a specially discounted three month summer pass. I always miss the boat on it unfortunately, but it's something like £50 poor three months unlimited play through the summer. As I say, I always spend about £25 in the cafe when I'm at soft play, so they make their money in that way too.
Lockers are important. As are loos and sinks that are child size.