This letter from the UK Minister of State for the Armed Forces is about the number of minors deployed to Iraq and Afghanistan since 2003. Under the terms of the Optional Protocol to the Convention on the Rights of the Child on the involvement of children in armed conflict (OPAC), by which the UK has been bound since 2003, it has been policy not to send armed forces personnel under the age of 18 to war zones, although the armed forces still recruit from age 16.
The letter states that seven personnel aged 17 years were sent to war zones – four to Iraq and three to Afghanistan – between 2007 and 2010. As far as the armed forces are aware, no minors have been sent to a war zone since 2010.
Although the letter says that it is unknown how many minors were deployed to Iraq or Afghanistan before 2007, at least some of this information is known. Fifteen 17-year-old personnel were sent to Iraq in error between 2003 and 2006. Seehttp://www.theyworkforyou.com/wrans/?id=2007-02-01b.117280.h It is not known how many personnel aged under 18 were sent to Afghanistan in this time.
Therefore, a minimum of 22 British armed forces personnel under the age of 18 have been sent to war zones since 2003.
It appears that most minors sent to war zones in error are returned to the UK within a few days, although one 17 year-old remained in Iraq for three months. See http://www.parliament.uk/business/publications/written-questions-answers-statements/written-question/Commons/2014-11-17/214739/
Download this letter here.