(a) to avert a risk of serious impairment or disruption of a family unit which would result in the placement of a child outside his own home;

(b) to enable a child who has been placed in a child care institution or other group care facility to be placed in a foster care setting more closely oriented to community or family life;

(c) to enable a child who has been placed in foster care to return to his family at an earlier time than would otherwise be possible. 3. If the child's family is able to pay part or all of the costs of day services, such family shall be required to pay such fees therefor as may be reasonable in the light of such ability pursuant to regulations of the department. 4. Day services may be provided by a social services official either directly or through purchase. Purchase of such services may be made only from a private non-profit corporation or association, except when the commissioner shall have approved the purchase of such services from a private proprietary facility by a social services official who has demonstrated a lack of conveniently accessible non-profit facilities that are adequate to provide the required services. 5. As used in this title, "day services" shall mean care and treatment for part of the day of one or more children under eighteen years of age and their families in a program which provides to such children and families in accordance with their needs various services such as psychiatric, psychological, social casework, educational, vocational, health, transportation and such other services as may be appropriate. Such services shall be provided in accordance with program standards promulgated by the department. Day services may be continued after the eighteenth birthday of a child in the care of an authorized agency and until he becomes twenty-one years of age. Day services shall not be provided to any children and their families for periods in excess of one year, without the approval of the department.