Dicky Birds in New Malden - not far from north kingston, especially if you have a car. My little girl goes there and they are excellent. Very nice staff, understanding, and unfazed by most things! I have one friend who took her daughter to asquith in Surbiton but withdrew her and put her in Dicky Birds Surbiton. One friend takes her boy to Dolphin kingston but isn't particularly overwhelmed with it and is looking to change. I don't have personal experience of either of these though, just hearsay.
I liked Little Stars near Norbiton station, but they were completely booked out and so it wasn't an option.