The said commission is authorized to return to the counties from which they were sent, the following classes of children:

     First, those who have become 16 years of age and who, for any reason, cannot be placed or retained in family homes.

     Second, those who by reason of vicious habits or incorrigibility, cannot be placed in or retained in family homes.

     Third, those who are of unsound mind or body, or have some physical disability, which prevents their being placed in family homes. Whenever a child shall be ordered by said commission to be returned to a county, as herein provided, the guardianship of the said commission shall cease, and the child thereupon becomes a charge on the county from which it was sent, and the superintendent shall report to the court the reasons thereof, and any other information which may assist the court in a further disposition of the child.