The sheer brutality of the violence unleashed against children is one of the hallmarks of today’s wars. About 350 million children are living in war zones from South Sudan and the Democratic Republic of the Congo to Syria and Myanmar. Many of these children are on the receiving end of war crimes and other human rights violations. Yet the world is turning its back.

Words cannot do justice to the moral depravity on display. Children are deliberately targeted for killing, abduction, rape and recruitment into armed groups. Others are treated as “collateral damage” in attacks on civilian infrastructure. Schools – and schoolchildren – are regarded as legitimate military targets. They are bombed in their classrooms or, especially if they are girls, assaulted for the crime of attending school. Obstructing humanitarian aid is now a standard military tactic, depriving children of access to food and medical aid.

Eglantyne Jebb, who founded Save the Children almost 100 years ago in the aftermath of world war one, once commented that “all wars are wars against children”. You can’t help wondering how she would view the wars of the 21st century.

What is happening to children is an affront to our shared humanity. It is also a violation of humanitarian laws, human rights provisions and norms established over more than a century, including the Geneva conventions, the Universal Declaration of Human Rights, and the Convention on the Rights of the Child. The principles and provisions underpinning these documents reflect the best of humanity. They are grounded universal rights and the simple but overwhelmingly compelling idea that even wars have rules – and that protecting children is a sacred responsibility.

The tragic reality is that the rules of war are now violated with near total impunity. Those committing crimes against children – from Russian and Syrian field commanders to the Saudi leaders driving Yemen to famine and Myanmar’s generals – operate without fear of international law, secure in the belief that they will never be held accountable for their actions. Is ours a generation destined to stand on the sidelines and wring its hands at the appalling images that remind us daily of the plight of children affected by conflict? Or can we challenge and overturn the culture of impunity surrounding those who harm children and make the current architecture of protection work?

‘Seven years of conflict in Syria have seen one in three schools damaged or destroyed, and half of the country’s children out of school.’ Photograph: Dimitar Dilkoff/AFP/Getty Images

That is the question asked Shaheed Fatima QC, one of the UK’s top barristers and an authority on human rights law. Her answer is delivered this week in the form of a 500-page legal report for the inquiry on protecting children in conflict – a forensic investigation into the rules, laws and norms designed to protect children in war that has been endorsed by leading human rights lawyers. Fatima’s argument can be summarised as follows: while concluding that the substantive legal protections for children threatened by armed conflict could be improved and strengthened in some respects, the key problem she diagnoses is not a deficit of rights. The real failing, beyond the deficit in political leadership to enforce the law, is a fragmentation of provisions across different treaties and institutions, compounded in some cases by ambiguity, making compliance, adjudication and enforcement more difficult.

Fatima advocates a single protocol that unifies the humanitarian law and human rights provisions protecting children, allied to the development of rules that bolster protection in key areas, such as attacks on schools and the obstruction of humanitarian aid. It is a report that should be read by anyone seeking to strengthen the protection of children affected by war. Of course, specific proposals will be debated. What is not open to debate is the urgent need for action. Headline numbers tell their own story. Last year, the UN secretary general expressed alarm at a sharp increase in the violation of the rights of children affected by conflict. Those violations left 10,000 children dead across a broad swathe of countries. More than 30 million children have been displaced.

What statistics cannot capture is the suffering and injustice experienced by so many children. Last August a guided bomb dropped by the Saudi-led coalition killed 40 children heading on a school trip. An attack that should have been investigated as a possible war crime has been dealt with instead through an inconsequential “internal inquiry”. Meanwhile, economic strangulation and the obstruction of humanitarian aid – a violation of the Geneva conventions – has pushed the country to the brink of a famine that threatens the lives of 400,000 children. The tragedy is that Saudi Arabia’s allies and arms suppliers – the US, the UK and France – have, until now, all but turned a blind eye to attacks on children, rendering the UN security council impotent.

‘What is happening to children in war zones is an affront to our shared humanity.’ Photograph: Sultan Kitaz/Reuters

Seven years of conflict in Syria have left one in three schools damaged or destroyed, and half of the country’s children out of school. Two years ago a Russian or Syrian air force jet bombed a school complex in Idlib, killing 22 children gathered in a school playground about to start their journey home. Once again, a possible war crime has gone unpunished – and once again the security council has been paralysed by political differences.

We need to ensure that more of these cases end up where they belong: in national and regional courts or in international courts, such as the international criminal court. In our increasingly fractured world, the international community is divided by many fault lines. The core principles of multilateralism, international cooperation and universal human rights are under attack from many quarters. But whatever the divisions, surely the world can come together in a common cause to protect children.

Martin Luther King once spoke of the “fierce urgency of now”. The children trapped in war zones surely have a right to expect and demand that we act with the urgency and resolve that human solidarity demands.

• Gordon Brown is the UN special envoy for global education and a former prime minister of the UK. This article was co-written with Kevin Watkins, CEO of Save the Children