The Princess of Wales is launching a campaign on one of her most personal causes – the "critical importance of our early childhood".
In an open letter, Catherine says not enough attention is paid to how children's first five years profoundly shape "the adults we become".
"I am absolutely determined that this long-term campaign is going to change that," the princess promises.
"They really are years like no other in our lives," she says.
This is the latest stage in the princess's long-standing efforts to raise the profile of the early years of children's development.
In a previous report for her Royal Foundation Centre for Early Childhood, the Princess of Wales warned how the roots of adult problems, such as mental health issues and addictions, often stretched back into the earliest years of life.
Research for the foundation showed almost two-thirds of parents with young children thought there was not enough support available for families at that stage.
The foundation called for workplaces to be friendlier to families with young children, to strengthen the early years workforce and give greater importance to children's emotional development.
The awareness-raising campaign, beginning this week, is now against the backdrop of worries about the cost of living – and last week the Prince and Princess of Wales visited a food bank in Windsor.
There are also public spending pressures, with teachers set to strike, and the campaign will emphasise the long-term value of investing in early years, with the backing of early years' experts, scientists and celebrities.
Neil Leitch, chief executive of the Early Years Alliance, said he wholeheartedly welcomed Catherine's engagement with this issue.
"For far too long, the early years has been deprioritised, disregarded and ignored when it comes to sector funding, despite a wealth of research showing that the first five years of a child's life are absolutely critical in shaping their long-term learning and development," he said.
"We hope that the princess's dedication to highlighting the importance of early childhood will prompt the government to sit up, take action and realise that education doesn't just begin when a child reaches the school gates," said Mr Leitch.
Next week the Commons education select committee will also be launching an inquiry into early years and childcare.
The cross-party group of MPs will consider whether parents have access to flexible and affordable childcare, with a recent survey showing 97% thought it was too expensive.
It will also take evidence on whether a reduction in Sure Start Children's Centres, providing support services for parents, has particularly affected disadvantaged families.
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