During her speech to supporters at the Battersea Arts Centre, Ms Swinson talked up her credentials as a prime ministerial candidate.
Liberal Democrat leader Jo Swinson has proposed "free universal childcare" for babies aged nine months until they start school.
Under the plans, working parents could receive 35 hours of free childcare per week.
The Lib Dems have also pledged to provide every child aged two to four with 35 hours of free childcare for 48 weeks of the year.
She said: "The choice for parents is simply not good enough. For so many people the cost of childcare means returning to work is impossible.
"How many of us know friends, usually women, who faced with astronomical childcare fees decide to stay at home instead of going back to their career? Maybe taking a couple of years out until the current free provision starts."
Ms Swinson said the policy would help close the gap between children from disadvantaged and wealthier backgrounds before they start schools and allow new mothers to go back to work.
The Lib Dem proposals would cost an estimated £14.6 billion annually, £8.6 billion more than what the Conservatives are planning to spend. It said it would be funded by reversing cuts to corporation tax and increasing capital gains tax.
Yet the Government says it will be spending more than £6 billion a year on childcare by 2020. Labour said it would invest an extra £4.5 billion in early years services.
Currently, parents of three- to four-year-olds are entitled to 15 hours per week of free childcare, with 30 hours available to those meeting strict criteria.
'I would be a better prime minister than Johnson or Corbyn'
She insisted that she could "do a better job as prime minister" if elected on December 12.
Ms Swinson said: "So while I look at what is on offer from Boris Johnson and Jeremy Corbyn, I know I could do a better job than then as prime minister."
She said the Lib Dems had better policies than what was on offer from "the tired two old parties led by men who want to rehash ideas from the past". She added: "Whether its the 1870s or the 1970s."
Photo credit: PA