A dependent child is aged under 15 or under 18 who is not working full-time.
"We found that parents generally get paid more than non-parents," Oakley said.
Mothers with dependent children earn more than $23 an hour on average, almost $1 an hour more than men and $2 an hour more than women without children.
According to international studies, mothers may get paid less than fathers because many women spend time caring for children, which interrupts full-time paid work.
Past New Zealand research suggests the effects of having children on a mum's pay rate may reflect breaks from work and reduced work experience.
Overseas research notes there is also potential for employers to discriminate against mothers, either knowingly or not.
Equal employment opportunities commissioner for the Human Rights Commission, Dr Jackie Blue said the report is an excellent example of why workplaces need to be looking to address what has caused the gender pay gap.
"The results of this research are not surprising, with several studies showing that the gender pay gaps rises markedly when women take on caring responsibilities. For women, it is virtually impossible to recover any ground they lose while taking on caring responsibilities," Blue said.
"This will continue until the culture within our workplaces changes."
"Organisations need to consider whether their own policies and practices are contributing to the gap, and if they are, they need to take leadership and provide flexible work options and supportive environments for women taking on caring responsibilities.
"They also need to develop policies that eliminate unconscious bias, discrimination and negative stereotypes in the workplace, if we are to close the gender pay gap," Blue said.
Blue said men also need to be encouraged to take on more child-rearing responsibilities.
"Providing paid parental leave for fathers would go some way to addressing this."
The Green Party's representative for women, Jan Logie, said the government needs to take decisive action to end the pay imbalance.
"Women have been underpaid for far too long, and we need a strong government that prioritises women getting a fair deal.
"When women are underpaid, it has a real impact on their partners and children, and the life they're able to create together."