Can I become an au pair with a WHV when I found a family through an online platform?

Hi, I’m 22, from Germany and plan to become a au pair in Australia. I’ve found host families on www.AuPair.com and was wondering if it’s legal to find a host family on an online platform. Because in the USA you definitely have to go through an agency. They give a lot of information about the program, but especially my mum is scared that something goes wrong.