2 mths - 18 mths 1:5
above 18 mths - 30 mths 1:8
above 30 mths - 3 years 1:12
above 3 years - 4 years 1:15
above 4 years - below 7 years 1:25
As far as I know, most childcare centres don't come close to the limit for K1 and K2 classes. I think it's because some parents prefer to take their children out and put them in kindergartens. They should not exceed the limit though.