(a) Dispositional hearing for delinquent or unruly child. If the court finds on proof beyond a reasonable doubt that the child committed the acts by reason of which he or she is alleged to be delinquent or unruly, it shall proceed immediately or at a later time to conduct a dispositional hearing for the purpose of hearing evidence as to whether the child is in need of treatment, rehabilitation, or supervision and shall make and file its findings thereon. If the child is to be held in custody at a detention facility between the adjudicatory hearing and the dispositional hearing, the court shall conduct the dispositional hearing within 30 days of the adjudicatory hearing. If the dispositional hearing is conducted more than 30 days after the adjudicatory hearing, the court shall make and file written findings of fact explaining the need for the delay. In the absence of evidence to the contrary, evidence sufficient to warrant a finding that acts have been committed which constitute a felony is also sufficient to sustain a finding that the child is in need of treatment or rehabilitation. If the court finds that the child is not in need of treatment, rehabilitation, or supervision, it shall dismiss the proceeding and discharge the child from any detention or other restriction theretofore ordered.

(b) Evidence. In dispositional hearings under subsection (a) of this Code section and in all proceedings involving custody of a child, all information helpful in determining the questions presented, including oral and written reports, may be received by the court and relied upon to the extent of its probative value even though not otherwise competent in the hearing on the petition. The parties or their counsel shall be afforded an opportunity upon request to examine and controvert written reports so received and to cross-examine individuals making the reports, except that portions of such reports not relied on by the court in reaching its decision which, if revealed, would be prejudicial to the interests of the child or any party to the proceeding may be withheld in the court's discretion. Confidential sources of information need not be disclosed.