Here's a little round up of swimwear for baby girls. Most of these brands do great boys swimsuits too.
1-4. Mini Rodini
5. Peppin Boutique
6. Old Navy
7-8. Pop Up Shop
Locally you can find some cute things at Country Road, Cotton On and Zodee. And for sun safe swimwear you can't go past Little Red Fish. If you want to spend big bucks (Baby Dior, Burberry etc. Not a great selection this season), then go here.