With the Aussie dollar as high as it is, I don't find much difference in price between Aus and HK nowadays. In fact, lots of things are actually cheaper in HK, never thought I'd say that.
I was recently in Australia and purchased nappy bin liners from a baby shop - they were AU$19.95 (about HK$120). Exactly the same product (same brand, size, etc.) is HK$55 in Mothercare !
Childrens clothes - I love Stanley markets and if you are living Southside, it will be convenient for you. You can buy lots of brand name clothes, fabulous quality, really cheap. For winter I brought my daughter an Osh Kosh tracksuit - HK$120, bargain.
Having said that, I always buy towels and sheets in Australia. HK seems to have either the very cheap or the very expensive, nothing in between. Nothing comparable to, say, Sheridan or Country Road.
If you are an average sized Aussie gal (over a size 10 Australian), you'll have trouble finding clothes anywhere except M&S. I always buy my clothes in Australia, and I'm not huge (size 12 Aust clothes, size 9 shoes). For example, last time I checked with Bally HK, they only stocked up to a size 8 shoe.
Good luck with the move