Most adults don't remember much of life before their second birthday. We don't remember if we slept a lot, how much we cried, or which foods we developed a taste for. We rely on what our family has told us.
Perhaps it's because of this that we can underestimate the importance of this period. Yet it's wrong to assume that what a person can't remember can't hurt them. The first 1,001 days, between conception and age two, are vital in shaping the health, wellbeing and life chances of every person. Neuroscience has shown that the first two years are the most important phase of brain development, with volume doubling in size. In just the first three months, the brain grows by 64 per cent, becoming more than half the size of the average adult brain.
This matters more than just from an anatomical perspective. Healthy brains are able to develop when babies have a loving, secure relationship with care-givers.
These relationships are the very foundation of our developing emotions and the cementing of the personality traits that will matter well into our adulthood.
While this period can be magical for families - holding and talking to a baby, for example, can form the most amazing lasting bond - it can also be one of the most difficult.
The arrival of a baby can cause considerable stress for parents, not least with any additional challenges such as balancing work and family life, or managing debt, substance abuse, or relationship problems.
These first 1,001 days enable infants to develop a secure attachment, shaping their early emotional wellbeing and substantially impacting on their social, economic and physical outcomes later in life.
That's why it's so important we do all we can to support parents, particularly as we learn more about the impact of poor perinatal mental health.
I have been an advocate for better early years support for more than two decades, so I was delighted when in June last year, the Prime Minister asked me to chair a cross-government Ministerial Group addressing this issue.
The group, comprising ministers from six departments, is looking at what more the Government can do to improve the support available to families in the critical period, to make sure every child has the best start possible.
I have since been touring the country to meet practitioners, academics, parents and babies. Speaking to these families reminds me how crucial this time is and demonstrates clearly the need to improve the support the Government offers for it.
On Friday, I was in Manchester, meeting parents and staff at Longsight Children's Centre, Home Start Manchester, the Big Life Group and Rusholme Sure Start Centre.
The need for such places, combining the efforts of both public and charity sectors, is clear. One-in-four mothers will experience mental health problems during pregnancy or in the first year after childbirth. Up to one in 10 fathers will also experience mental health problems. So the more we can do for both parents, the better start they can have with their baby.
A complicating factor for families is the unknown cause of postnatal depression. There are some obvious triggers - where there is a history of poor mental health, a lack of support, an abusive relationship or recent trauma. But even for parents where none of these factors apply, postnatal depression can creep up and be hugely destabilising. And the sad irony is that this period of new parenthood is expected to be one of the happiest of our lives.
Aside from the clear impact on the individual affected and their family, perinatal mental illness also has a significant impact on the economy. It is estimated that every year, the long-term cost of failing to address effectively new mothers' mental health is £1.2 billion to the NHS and social services, and £8.1 billion to society.
Simply put, better mental health care and early intervention aren't just good for those affected. They are good for everyone.
This is a priority area for the Government and we are making significant progress. The recent Long Term Plan for the NHS unveiled fresh perinatal mental health support for new mothers and their partners, and extended the length of time that support can be accessed to two years from their child's birth.
While these are steps in the right direction, there is some way to go until we can be sure that every family will know how to access the support they need.
In Manchester, many of the parents I met spoke of how lonely they had been after the birth of their child and the toll this can take emotionally.
I applaud the Sunday Express, which has campaigned tirelessly for increased mental health support. My own ambition is for us to always remember that good mental health begins at the beginning - in our earliest years.
My cross-Government group is working to collectively consider not only how we can achieve good perinatal mental health but how we can help to prevent these crises in the first place.
I truly believe that by providing world-class support in these critical early years, we will create a generation of much happier, securely attached babies and young people.