1. A decree of the juvenile court made under the provisions of section 211.181 may be modified at any time on the court's own motion.
2. The juvenile officer, the parent, guardian, legal custodian, spouse, relative or next friend of a child committed to the custody of an institution or agency may, at any time, petition the court for a modification of the order of custody. The court may deny the petition without hearing or may, in its discretion, conduct a hearing upon the issues raised and may make any orders relative to the issues as it deems proper.
3. The authority of the juvenile court to modify a decree is subject to the provisions of chapter 219.