The islamist militant group (Boko Haram) has forced children into their ranks in Nigeria.
The Democratic Republic of the Congo had child soldiers during their two civil wars.
Yemen has also had thousands of boys fighting in its many wars.
Campaigns like Children, not Soldiers are being formed to stop the recruitment and use of child soldiers in conflict. Other organizations are Child Soldiers International and Invisible Children.
The UN wants to give child soldiers rehab after the tragic thing that they have had to do while fighting.