Dominic Ongwen’s trial, which begins in earnest on Monday, is one of the grimmest and most morally complex that the international criminal court has tackled. The body exists to try the worst offences: genocide, crimes against humanity and war crimes. It is not the horrifying list of charges, including rape and murder, that makes Mr Ongwen’s case unusual, but that he is believed to be the first former child abductee to be tried. Seized as a 10-year-old, and forced into violence, the former commander of the notorious Lord’s Resistance Army has denied all offences and insists that he is the victim.

His lawyers have indicated that duress may form part of his defence; others say he must not avoid justice for acts committed as an adult, but acknowledge that his experience may be relevant in mitigation of a sentence. The judges must not only ascertain the evidence against the 40-year-old, but also consider what he first endured and the mind control techniques and sheer brutality that the LRA has used on the 30,000 to 60,000 children it has abducted over its history. The more pressing issue highlighted by the trial is what to do about the tens and perhaps hundreds of thousands of children still associated with armed forces and armed groups worldwide, used as combatants and in other roles, including as porters and spies.

Occasional pieces of good news, such as the release of 145 child soldiers by rebel groups in South Sudan last autumn, are dwarfed by the scale of the problem: according to Unicef, government and opposition forces there have taken on 16,000 children over the last three years. In the worst cases, children not only face horrific abuse and risk death – at the hands of rival forces or their captors – but, if they escape, are traumatised and poorly equipped to re-enter society even if peace prevails.

Campaigners say a first step would be action at home, agreeing to what the NGO Child Soldiers International calls the “straight-18” standard, a minimum enlistment age of 18 for state forces. Two-thirds of states worldwide have done so (even if they don’t always abide by their own rules) yet the US permits recruitment from 17 and the UK from 16, in both cases dependent on parental consent and with the caveat that under-18s cannot be sent to war. This is unquestionably different from beating and drugging an 11-year-old until they will fight for you. But it is still wrong. A state that stops 16-year-olds from seeing the most violent films should not begin training them to kill. A “straight-18” rule would send a clear message that child soldiers are unacceptable.

Secondly, governments can exert pressure on others; the US, Belgium and Switzerland have tied military aid to ending child recruitment. A “national interest” clause means the American law is honoured more in the waiver than the observance. But Human Rights Watch believes its use prompted the government of the Democratic Republic of the Congo to largely end the recruitment of child soldiers, demonstrating why the US should make better use of it and others should consider similar legislation.

Persuading armed groups is a harder task, and in some cases no doubt impossible. Islamic State forces young children into violence for propaganda as well as for military purposes and to brutalise a generation. But some groups have proved willing to change because they seek international recognition, or fear they could one day face legal repercussions – with commanders even asking NGO staff if they could “end up in the Hague like [Thomas] Lubanga”, convicted of recruiting children in 2012.

Thirdly, existing victims must not be written off. Rehabilitation and reintegration programmes are often scarce, seriously under-resourced, short-term and uncoordinated. They do not come cheap: in the DRC, economic and professional reintegration of each child soldier costs an estimated $1,000 a year. Yet abandoning traumatised and stigmatised children, often without education and family ties, is vastly more costly. They may hurt themselves and others in civilian life. They may return to armed groups or forces because they lack an alternative. They may drag others in; the charges against Mr Ongwen include recruiting and using children in combat.

The problem cannot be seen in isolation. Peace is the best protection for children. But helping to reintegrate those who have already been exploited is crucial to the long-term prospects for peace and security in their societies.

This is a Guardian editorial which appears on the Guardian website.

Banner image: Dominic Ongwen at his first appearance before the ICC on 26 January 2015, © ICC-CPI.