The Australian Royal Commission into Institutional Responses to Child Sexual Abuse, among the recommendations of its final report
The Australian Catholic Bishops Conference should consult with the Holy See, and make public any advice received, in order to clarify whether:
a. information received from a child during the sacrament of reconciliation that they have been sexually abused is covered by the seal of confession
I am not aware of any explicit communication on this subject, and this recommendation is also not directly addressed by the Apostolic Penitentiary's Recent Note on the Seal of Confession, but the Note does touch upon the issue. It says "Should there be a penitent who has been a victim of the evil of others, it will be the concern of the confessor to instruct him regarding his rights as well as about the practical juridical instruments to refer to in order to report the fact in a civil and/or ecclesiastical forum to invoke justice."
In fact, the situation is somewhat complicated. For reasons of natural shame, and because perpetrators often actively try to make the victim feel guilty for the crimes committed against him or her, so that he or she will be ashamed to speak, child victims of sexual abuse often have feelings of guilt, and might well confess the abuse as though it were a sin. In this case, the sacramental seal would seem to apply directly. Moreover, even if the child does not mention it as a sin, and it would not fall under the seal as such, various consequences undesirable for the child might arise were the priest to reveal that information, and so the priest would be forbidden from doing so. (According to a decree of the Holy Office of 1682, knowledge from confession cannot be used if the use is harmful to the penitent, even if greater harm for the penitent follows from failing to use that knowledge)
The Church's tradition has recognized the possibility of a penitent's releasing a priest from the seal of confession (St. Thomas Aquinas, e.g., affirms the possibility, and canon law of 1917 refers to it), and this note itself makes reference to it in the limited case of a penitent's giving a priest permission to talk about what was said in confession outside of confession. The simplest and best solution to aim for, in many cases, might be for the priest to get permission from the child to tell others about the matter. For some reason, however, the apostolic penitentiary seems not to want to mention this possibility.