Your congregation's director of Religious Education should provide the official number of those enrolled in Religious Education. The Unitarian Universalist Association (UUA) asks for this statistic each year as part of congregational Certification of Membership.
Religious Education enrollment totals should equal the number of children and high school youth who are registered within the congregation's religious education program. For safety reasons, the UUA suggests that all children in the program be officially registered. If you need help designing a registration system that works for you, please contact your district staff.
If there are children and high school youth who attend Religious Education but are not yet officially registered, you may include them in your total count. But please make a point of registering everyone so that reported totals in the future will include only those children and high school youth who are enrolled.