It is primarily the duty of parents and those who take the place of parents, as well as the duty of pastors, to take care that children who have reached the use of reason are prepared properly and, after they have made sacramental confession, are refreshed with this divine food as soon as possible. It is for the pastor to exercise vigilance so that children who have not attained the use of reason or whom he judges are not sufficiently disposed do not approach holy communion.
Source: Code of Canon Law (Vatican.va)