A/HRC/21/25 16. There are additional groups of children, often overrepresented in the criminal justice system, who should not be there, and for whom appropriate care and protection services should be provided. These include children with mental health problems, children with substance abuse problems, children in need of care and protection and unaccompanied children. By removing such children from the criminal justice system the potential to reduce violence against them is clearly increased. 17. Many States still have low minimum ages of criminal responsibility (MACR). The Committee on the Rights of the Child has encouraged States parties to increase their lower MACR to the age of 12 years as the absolute minimum age and to continue to increase it to a higher age level. This is the absolute minimum that must be progressively increased. States setting a higher MACR must also have a clear policy on non-custodial measures for the vast majority of children who are below that age, to avoid them being transferred from one form of custody to another. Age thresholds for detention are also a good mechanism for keeping children out of detention, particularly prison, and this can be set higher than the MACR.10 18. A key principle of a rights-based juvenile justice system is non-discrimination. Children from ethnic and minority groups are overrepresented in the criminal justice system. Similar situations occur with migrant children and asylum seekers who are placed in detention on the basis of their migratory status. The reasons for this may include discrimination by law enforcement officials, but also social exclusion experienced more generally by those groups in the countries where they live. Social exclusion tends to result in patterns of poverty, domestic violence, gang activity, substance abuse, barriers to education, and poor prospects for meaningful employment. 19. An important and highly effective way of reducing the number of children in the criminal justice system is through diversion mechanisms, such as restorative justice programmes and alternative non-custodial measures. Although these children may still be at risk during the police station phase, pretrial diversion avoids pretrial detention. Alternative sentencing that prevents children from being deprived of their liberty is invaluable in the reduction of violence against children. IV. Identification of risks of violence within the juvenile justice system A. Law enforcement activities 20. Although contact with the juvenile justice system usually begins with arrest or apprehension, children can be victims of violence through law enforcement activities that never result in arrests or charges. Concern is expressed that anti-social behaviour reduction methods such as dispersal powers may lead to the use of violence, especially as a certain amount of force is permissible by law. B. Apprehension and arrest 21. Police and other security forces are often responsible for violence against children, and arrests are one of the situations in which this occurs. The Five years on follow-up 10 6 T. Liefaard, Deprivation of Liberty of Children in Light of International Human Rights Law and Standards (Intersentia, 2008).