The board of directors of any school district shall have the power to establish and maintain preschools and to provide before-and-after school and vacation care in connection with the common schools of said district located at such points as the board shall deem most suitable for the convenience of the public, for the care and instruction of infants and children residing in said district. The board shall establish such courses, activities, rules, and regulations governing preschools and before-and-after school care as it may deem best: PROVIDED, That these courses and activities shall meet the minimum standard for such preschools as established by the United States department of health, education and welfare, or its successor agency, and the superintendent of public instruction. Except as otherwise provided by state or federal law, the board of directors may fix a reasonable charge for the care and instruction of children attending such schools. The board may, if necessary, supplement such funds as are received for the superintendent of public instruction or any agency of the federal government, by an appropriation from the general school fund of the district.