Sounds like you are doing a fab job! There is a class type set up in Melbourne called Concept kids which is a preschool science type program. Lots of talk about space and 'how' things work. Also Braintastics which teaches reading/phonics. Not sure if this is too structured for you? I have found lots of value in some cheap art sets in Kmart, or some more exxy kits at the National Geographic shop. Also we've painted a few bits of furniture from the oppy as well.