Hello
We recently went to a 4th birthday party for DD's freind at Jupiter Jo's in Ewell, which isn't too far from Kingston. It was brilliant and both my kids, 4.5 year old DD and 2.5 year old DS just loved it.
It's one of these softplay areas where you can climb and slide down. If you search for them on Google, there's a pic of it.
The other mums were mostly sat at the tables but I was mostly in the apparatus, which was great fun.
There were tables for the adults to sit at, a little kiosk selling snacks and drinks and a separate party room for the kids to have their party lunch.
DD is allergic to loads of things and I tend to avoid soft play areas as they usually have kids tearing around with food, which is a nightmare for me, but the soft play area was very clean so we'll definitely go again. You can go and play as well as have parties there, so definitely worth checking out.
Hope this helps and that you find a lovely venue and that your granddaughter has a lovely birthday.