Assignment of Staff. One or more family child care teachers shall be assigned to each group of children as needed to meet the requirements for group size and staffing set forth at §§C—G of this regulation. Age of a Child. For purposes of determining group size and staff required under this chapter, the age of a child is determined solely according to the date of the child's most recent birthday. Same-Age Groups. In a group of children of the same age, the following staff/child ratio and maximum group size requirements apply: Groups of Children Younger than 2 Years Old. In a group of children where each child is younger than 2 years old, the following staff/child ratio and maximum group size requirements apply: Mixed-Age Groups with Children Younger than 2 Years Old. In a group where children younger than 2 years old are mixed with children 2 years old or older, the following minimum staffing levels and maximum group size requirements apply: Mixed-Age Groups with Children 2 Years Old or Older. In a mixed age group with children who are 3 years old or older, the staff to child ratio is 1 to 10. In mixed-age groups of varying sizes that include children who are 2 years old, the following minimum staffing levels apply: Group Size and Staffing in Approved Educational Programs. During a school day approved by the Department, a teacher shall be assigned to each class and the following requirements apply: A nursery school may not exceed a staff/child ratio or group size requirement set forth at §G(1) of this regulation, except that a Montessori school that has been approved by the Department may exceed a staff/child ratio or group size requirement by no more than 1/3. When children who are 2 years old, 3 years old, 4 years old, and 5 years old are grouped together, the average age of all the children in the group as of September 1 of that school year is used to determine the group's maximum size and staff/child ratio.