In all districts maintaining grades 1 to 8 or 1 to 12, to establish nursery schools for the instruction of children between the ages of 2 and 6 years, if, in its judgment public interest requires them and sufficient funds obtained from local and federal sources other than local district taxes are available to pay the necessary expenses thereof; provided, that the school board shall at all times have complete jurisdiction and control over such schools, including the employment of teachers, attendants and any other employees, and shall have complete control of the expenditure of such funds in connection with the establishment and maintenance of such schools.