Julie
If you have return tickets, most airlines will not give you the double baggage allowance even though you are travelling on a hitherto unused
PR visa. Their view is that if you have return tickets then you are not emigrating at the time when you first use the new visas. Airlines charge about £20 per kg for excess baggage so I would recommend caution about this.
With regard to the food for Chloe, please see the following links:
http://www.daff.gov.au/__data/assets...canti_take.pdf
What can't I take into Australia? - DAFF
By far the easiest "rule of thumb" with entering Australia is simply to leave all uneaten snack food on the plane and be done with it. When you are tired after a long journey the last thing you need is hassle at Customs in Perth.
Best wishes
Gill