Another thing to consider is the language support at home - this is my personal opinion only, but If your kids are going into primary then they would be on 75% putonghua at school, and I think it would probably follow then that parents ( either or both) would need to be quite conversant in chinese/putonghua if they are to help their kids in this area. I have seen some of the children's work, and I must say as someone who has studied chinese from early years on, its not for the faint hearted.
Class size for foundation /primary is around 15 but I hear it sometimes is larger ( around 18-20 max??) , but there are around 5 classes at the early years ( if I remember correctly). You really need to visit the school to get a feel for what it is like.