According to the website of Human Rights Watch hrw.org/ :

"In over twenty countries around the world, children are direct participants in war. Denied a childhood and often subjected to horrific violence, an estimated 200,000 to 300,000 children are serving as soldiers for both rebel groups and government forces in current armed conflicts."

The military use of children takes different forms: they can take direct part in hostilities (child soldiers), they can be used in support roles such as porters, spies, messengers, look outs and sexual slaves; also they can be used for political advantage either as human shields or in propaganda.

Special thanks to Silverdrake Sparrow for her help.