I would say it is the most primal societal bias. We spend so much time with our parents when we are young that they become our benchmarks. Even an absent mother or father can still have a large impact on us.
I do think that a set of parents that treat each other as equals will probably lessen sexism... but not rid us of it. To give an example.. say you have a parent that is always late for things. As the child grows older, they have a subconscious bias that expects that gender to always run a little late.