Section 68B. The department of youth services may use or provide special foster homes and places of temporary custody commonly referred to as detention homes, at various places in the commonwealth which shall be completely separate from any police station, town lockup or jail, and which shall be used solely for the temporary care, custody and study of children committed to the care of the department of youth services. The commissioner of youth services may at his discretion transfer any child thus committed from any foster home or detention home to another such foster home or detention home.