What fun! Australia, the sunburned country (but in a good way). I adore Australia and would love to go back sometime. Anyhoo, I am familiar with the trek across the skies and here are my suggestions for travel attire:
Layer, Layer, Layer! Just like living here in the San Francisco area, you need to dress for summer and plan for winter. First of all, ditch the Juicy sweatsuit - unless you are Kate Gosselin, but since you are traveling with just a single one-year-old I assume you aren't. Velour travel sweats are très passé -- it's definitely time to donate them to a good cause.
I would go with a pair of very comfortable jeans with a little stretch to them. Something slouchy, like the new boyfriend style denim. Add a great fitting tee shirt - perhaps something with a little feminine style to offset the slouchy jeans. Top with the au courant denim jacket or a shrunken blazer.
For footwear, go with a pair of stylish skimmers or driving mocs (super comfy!) Keep an additional tee shirt or two in your carry on bag in case of spills or baby dribbles. (As the mommy of an adorable one-year-old I am sure you have this little tidbit of advice down pat!)
The thing to remember when travelling for long periods of time is that it is very important that you be comfortable and not wear anything that is too restricting. No tight denim or cinching waistbands. Move around often so avoid dead limbs, and more importantly to avoid the possibility of blood clots (been there, done that, spent a month in the hospital!)
Have a fabulous time in Australia!
She She Me