Section 56B. Any judge of a probate court may appoint a guardian ad litem to institute contempt proceedings under the provisions of section thirty-four A against any party for failure to obey judgments of the probate court involving care, custody or maintenance of minor children, and said guardian ad litem may personally serve throughout the commonwealth any summons or capias incidental to the enforcement of this section. The compensation shall be fixed by the court and shall be paid by the commonwealth, together with any expense approved by the court, upon certificate by the judge to the state treasurer. The state police, local police and probation officers shall assist the guardian ad litem so appointed, upon his request.