Jeremy Corbyn is expected to use his conference speech in Liverpool to pledge an expansion of free childcare.
Labour has previously said it would offer 30 hours of "genuinely free" childcare to all parents of two, three and four-year-olds in England.
Mr Corbyn will say Labour will also offer extra, means-tested subsidised hours on top of this allowance.
These will be free for the poorest households and cost no more than £4 per hour for higher incomes, Labour says.
Currently most working parents in England and Wales are entitled to 30 free childcare hours for three and four-year-old children during term time.
Campaigners say this has left some childcare providers struggling to remain open because of increased running costs and a lack of government funding.
Mr Corbyn will say the current offer is "free in name only", describing Labour's "universal" offer as a "vital and long overdue change".
He will also promise to improve the pay and skill levels of childcare staff.
"Opportunity matters most in the earliest years of life," he will say.
"It is a crucial time to open up children's life chances. Driving up standards of childcare will make that vital difference for millions of our children."
Households where a parent earns more than £100,000 are also not currently eligible for free child care.
Labour say the plans will cost £4.5bn.
It would be paid for, a spokesman said, by "taxes on the top 5% of earners and big companies".
CBI deputy director general Josh Hardie said: "Business has long called for support to parents to make childcare more affordable.
"The challenge will be to find ways to fund affordable childcare sustainably and sensibly. The prize will be significant for working families across the UK and can play a serious role in reducing the gender pay gap."
Children and families minister Nadhim Zahawi, responding for the Conservatives, said it was another "unfunded promise" from Mr Corbyn.