Section 21. The following words and phrases when used in sections twenty-two to fifty-one F, inclusive, shall, unless the context otherwise requires, be construed as follows:—

“Department”, the department of social services.

“Parent”, means mother or father, unless specified parent as defined under section one of chapter one hundred eighteen.

“Child in need of services”, a child below the age of seventeen who persistently runs away from the home of his parents or legal guardian, or persistently refuses to obey the lawful and reasonable commands of his parents or legal guardian, thereby resulting in said parent’s or guardian’s inability to adequately care for and protect said child, or a child between the ages of six and sixteen who persistently and wilfully fails to attend school or persistently violates the lawful and reasonable regulations of his school.

“Custody”, shall include the following powers: — (1) to determine the child’s place of abode, medical care and education; (2) to control visits to the child; (3) to consent to enlistments, marriages and other contracts otherwise requiring parental consent. In the event that the parent or guardian shall object to the carrying out of any power conferred by this paragraph, said parent or guardian may take application to the committing court and said court shall review and make an order on the matter.

“Evidence”, shall be admissible according to the rules of the common law and the General Laws and may include reports to the court by any person who has made an investigation of the facts relating to the welfare of the child and is qualified as an expert according to the rules of the common law or by statute or is an agent of the department or of an approved charitable corporation or agency substantially engaged in the foster care or protection of children. Such person may file with the court in a proceeding under said sections a report in full of all the facts obtained as a result of such investigation. The person reporting may be called as a witness by any party for examination as to the statements made in the report. Such examination shall be conducted as though it were on cross-examination. Evidence may include testimony of foster parents or pre-adoptive parents concerning the welfare of a child if such child has been in the care of the foster or pre-adoptive parents for six months or more, and may include the testimony of the child if the court determines that the child is competent and willing, after consultation with counsel, if any, to testify.