Ms Bishop is backing the 'Thrive by Five' campaign - spearheaded by epidemiologist Fiona Stanley and philanthropist Nicola Forrest - calling for a universal, high-quality early learning system.

The campaigners have penned an open letter to the Morrison government calling for improvements to the childcare sector for the benefit of both children and parents.

The letter points to research saying 90 per cent of a child's brain can be developed by the age of five, highlighting the need for intellectual and social development by then.

"The quality of the physical and social environments during those years both at home and in the early learning system is vital to a child's healthy development," the letter says.

"Sadly, many children who enter the school system developmentally vulnerable never catch up with their peers. If a child starts behind, they stay behind."

The group estimates hundreds of thousands of parents could re-enter the workforce if childcare was more affordable, particularly helping mothers.

Former Australian of the Year and anti-domestic violence campaigner Rosie Batty and previous SA Labor premier Jay Weatherill are also supporting the campaign.

The letter says families and early educators are bearing the financial weight of the system, with childcare costs some of the highest in the OECD.

"It is often the major cost of living pressure and for many the cost is too high, and they are locked out of the system completely."

The Morrison government temporarily made childcare free across Australia during the coronavirus pandemic, which the group says showed the value of affordable, accessible early learning.

"Let's make children, women, families, educators, and our economy the winners by delivering a new early learning and childcare system for Australia."

Australian Associated Press