Delegates meeting in Berlin, at the first European Conference on Child Soldiers have called for a ban on all under-18s joining the armed forces.
While more than 20 European countries allow under-18s to be recruited into their armed forces, the United Kingdom comes in for particular criticism.
It has more than 6,500 children in its armed forces. Under-18s may not be recruited to Britain's police force but in Kosovo, some 50 under-age Britons are serving with KFOR, the peace-keeping force.
Under-age Britons were among the first into the capital, Pristina.
There is particular concern about the treatment of children in the British forces. Since 1982, more than 90 16 to 17-year-olds have died during service.
Other countries - including Estonia, Finland, France, Germany, Italy, the Netherlands, Norway, Poland and Spain - allow 17-year-olds to join their armed forces. However France, Italy, Norway and Spain are in the process of ending recruitment of minors.