Competition in professional sports should not depend on the age of the participants, only on the skill level they display. Children should of course require parental consent and should not be forced into participation, but any child who is talented enough to compete with the adults should be given the opportunity to show their extraordinary abilities.
Children be allowed to compete in professional sports because they are not professionals. Children should focus on going to school and socializing with people their own age. Parents should not give their children adult responsibilities. Children should only play sports for entertainment and to get physical exercise for their well being.