Young combatants, who would be considered children by today's standards, were occasional warriors in medieval battle. In an online article Teenagers at War During the Middle Ages, Kelly DeVries looks at the roles of such youth in combat as the Black Prince and Joan of Arc and why they were so unusual.
Recent forensic evidence shows that most medieval soldiers were not the youth of legend, but seasoned fighters.
Judging from what little age-related evidence there is, however, this may actually not have been the case. In fact, the children of the Children's Crusade may not actually have been children, or even adolescents, while the young age of the Black Prince and of Joan of Arc may have been unusual in leadership roles, but seems not to have mattered as the two youths showed military skill far beyond their teenage years.