By the time a little girl or boy walks across a playground or field and steps into a classroom for the first time - no matter where it is in the world - it may still be too late for them to fulfill their potential.
Why? A child's brain is 90% developed by the time they reach their FIFTH birthday. That means the most important phase in their life WOULD already have happened - the steps that lay foundations for success at school and in later years.
To allow the brain to grow and children to develop to their full potential, they need five key elements of quality, nurturing care - including play, health, protection, nutrition and early learning. Without it, children are at risk of lifelong consequences.
So, a simple enough equation, with scientific evidence to back it up, yet governments the world over don't seem to have grasped it.
Access to pre-primary education can have a significant impact on a child's future prospects in education and later adult life. It's particularly vital for the most marginalised young children in the poorest countries.
In Mozambique, for example, children in rural areas who enrolled in pre-school were 24% more likely to go on to attend primary school - and show improved understanding and behaviour - compared to children who had not.
Supporting early learning is a smart investment - every $1 injected into early childhood care and education can lead to a return of as much as $17 for the most disadvantaged children. It reduces inequality in the education systems and leads to better outcomes for all children.
However, a new report published this week by Theirworld shows that despite all the evidence that pre-primary education is vital, millions of children are still missing out on the chance of a proper start in life.
Access to pre-primary education continues to be a lottery, dependent on where a child is born. 85% of children in low income countries do NOT have access to pre-primary education. Compare that with high-income countries, where 82% ARE in pre-primary schools.
A child born in the Latin American and Caribbean region is more than twice as likely to be in pre-primary education than those born in sub-Saharan Africa.
On current trends, the International Commission on Financing Global Education Opportunity says 69% of school-aged children in low-income countries are not expected to learn basic primary-level skills by 2030.
Millions more will simply not attend school or drop out of classes. Those who do stay on are less likely to have good learning outcomes, are unlikely to complete secondary education and extremely unlikely to make it to higher education. The end result? An uneducated workforce will impact on communities and countries, affecting potential for growth.
Much of the blame for this situation lies in the lack of investment in pre-primary education, which is staggeringly small. Low income countries spend only $8 a year on pre-primary education for each child - less only two cents a day. That amounts to an average of only 2% of total education spending for low income countries.
The paltry amounts of funding for early education cannot deliver on the promises made by world leaders.
And when it comes to international donor governments giving a proportion of their aid money to pre-primary education, the picture is equally depressing. There is no major bilateral donor champion of pre-primary education and even multilateral funders are falling short.
A far greater proportion of resources needs to be targeted towards pre-primary education. This means a new approach to funding is needed to tackle the problem. It is time for governments and the international community to back up their words with actions.
If they believe early child care and education is important - they must prove it. Prioritise it in education policies and allocate sufficient resources to get EVERY child in EVERY country into free, quality pre-primary education.
Sarah Brown is president of Theirworld and executive chair of the Global Business Coalition for Education