A child’s most important steps happen before they set foot in a primary school. By their fifth birthday, their brain will already be 90% developed and the foundations for success at school and in later life will be in place.

However, despite all the evidence that pre-primary education is vital, millions of children continue to miss out on the chance of a great start in life. Access to pre-primary education continues to be a lottery, dependent on where a child is born.

In 2016 World Bank experts said money spent on early childhood development is “the smartest investment a country can make … If a child gets the healthcare, nutrition, affection, stimulation, and education that she needs – the gains she makes in those early years are hers for life.”

But research published on Wednesday by children’s charity Theirworld reveals that development spending – aid – is missing out education for young children. Despite increases in funding for early childhood development, just 1% of aid for under-sixes goes to education, putting millions of children at a disadvantage before they even start primary school.

Support for learning is the best investment a government can make, for the child, their community and country. It reduces inequality in education and leads to better outcomes for all. This is why governments around the world agreed the sustainable development goal target that by 2030 all children should have access to quality early childhood development, care and pre-primary learning “so that they are ready for primary education”.

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But the reality is that the lack of equitable access to pre-primary education means more than 200 million children aged five and under in developing countries are at risk of failing to reach their full potential.

This means inequality within a country starts at a very young age. For example, in Ghana, a boy from a wealthy household and urban area is more than twice as likely to attend pre-primary school than a girl from a poor household who lives in a rural area.

The evidence also shows that the benefits of early years education are greatest for the most marginalised and disadvantaged, including children with disabilities, those with HIV and Aids, or those caught up in conflict or disasters. These young people are often the least prepared for primary school or most likely to miss out on the opportunity completely.

It’s time to end this inequality. And when we do, the benefits will be obvious, not just to the children, but to society as a whole. Children from marginalised backgrounds who attend quality pre-primary care are more likely to enrol and stay in school, which has a positive impact on learning all the way into secondary education.

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 to show improved understanding and behaviour, compared with children who had not.

Many countries have already committed to getting every child into pre-primary but more can take this step. International aid donors can do more to support such efforts.

If national governments, aid donors and World Bank and other institutions set a target of 10% of their education budgets going to pre-primary projects, we would start to see the commitments to the youngest children matched with actions.

In the past 15 years, high-profile global initiatives have led to transformations in the funding going to health and nutrition for children from birth to five years, with ground-breaking research, commitments of world leaders at the G8 and top international donors becoming champions of these causes. The results are showing in the lives of children around the world.

But pre-primary education has seen a conspicuous lack of support both in terms of attention and financial support. It may be because the results of this investment are not as immediately visible as those for health and nutrition. However, every country that has provided free, quality pre-primary education for all as the foundation of a child’s learning journey has seen the results, in educational attainment, future earnings and wellbeing of their family – especially for those girls and boys from the poorest backgrounds.

If the international community is serious about tackling inequality then they need to start investing in pre-primary education.