I would like to know, which Act defines the rules abut the determination of a father in Australia. I can find the rules on different websites, but not the source, which law it is.

https://www.legalaid.vic.gov.au/find-legal-answers/child-support/proving-who-dad-is

Sometimes there is disagreement as to who is the father of the child. The law says that a person is the biological father of the child if:

Which law? Which act?

Same rules here: https://www.legalaid.qld.gov.au/Find-legal-information/Relationships-and-children/Child-support-and-maintenance/Proof-of-parentage#toc-disagreements-about-who-is-the-child-s-father-2

The law says a person is the child’s biological father if:

Which law?