Personal recommendations are definitely very good to get.
I also strongly suggest popping in at totally random times at the school to get a feel for what really goes on. Call them and set up an initial appointment where someone can walk you through the school and explain things, but then also ask if you can pop in a few times without notice. If they say no, then ask why and definitely doubt the place. If they say yes then pick 3 days, 3 different times, and rock up unannounced. Not normal times when they're expecting parents. So go at like 10am, 2pm, and 4pm or something. That way you'll see what happens when they're not expecting anyone to be watching.
If it's at all possible to see inside the grounds from the outside you could also stop and watch from the outside during playtime, that way they might not even be aware that they're being watched.