Just to put a 'risk dampener on this sorry :sorry: It isn't recommended that polystyrene be used near the under 3's (or older) because of the Choking hazard it posses and the fact that wind pipe blockages can't be detected by Xray!
This was the main reason why Bean bags were not allowed in our preschool or primary school library/classroom.
Of course, substituting the polystyrene balls for other types is good
