No person who is a member of the board of trustees or a member of the immediate family of a member of the board of trustees of any school district shall be employed by the board as a teacher without the written approval of the board of trustees of the district and, when applicable, of the board of education of the county, or unless a majority of the parents or guardians of the children attending the school for which such teacher is employed requests such employment in writing. The provisions of this section shall not apply to any teacher who was employed prior to the time he or his family member became a board member. For purposes of this section, the immediate family of a member of the board of trustees shall include only his parents, children, brothers or sisters. Provided, that the provisions of this section shall not apply to school bus drivers.