Resources within the home are distributed unequally along gender lines
The claim that differential resource allocation between boys and girls is 'just how it works' appeals to tradition to justify what is in fact an unequal and potentially discriminatory practice. The naturalistic fallacy holds that because something has been a certain way, it is therefore correct. Both of these fail because law and ethics require us to examine whether a practice is fair — not merely whether it is familiar.
They say: 'This is our house and our rules — we decide who gets what.' You respond by: Affirming parental authority in principle while introducing the Children's Act's best interests standard as a legal framework that applies within the home.
After you give your response, they may push back. Here is how to handle each counter-argument.