We had a large one (1.5m * 1.5m) as I didn't want DS to feel "cramped". But DS1 would only ever go in it if I was in there with him. So needless to say it wasn't much use for him. But it was fantastic for DS2. It meant one of them could be in and one out (DS1 would go in by himself by then) and I knew the baby was safe. Even after DS1 learnt to climb in/out, it was still quite useful because he seemed to love being there as an older child - go figure!