After a petition shall have been filed and after such further investigation as the court may direct, in the course of which the court may order the child to be examined by a physician, dentist, psychologist or psychiatrist, the court may dismiss said petition or may issue a summons reciting briefly the substance of the petition, and requiring the person or persons who have the custody or control of the child, or with whom the child may be, to appear personally and bring the child before the court at a time and place stated: Provided, That the court in its discretion may excuse but not restrict children from attending the hearing. If the person so summoned shall be other than the parent or guardian of the child, then the parents or guardian, or both, shall also be notified of the petition and of the time and place appointed for the hearing thereon, by personal service before the hearing, except as hereinafter provided. Summons may be issued requiring the appearance of any other person whose presence, in the opinion of the judge, is necessary.

     Any interested party who shall voluntarily appear in said proceedings, may, by writing, waive service of process or notice of hearing.