What is the prescription of a criminal action against perpetrator of crime against minors

The extension of the term of prescription of a criminal action to twenty years, maintaining the right of the Congregation for the Doctrine of the Faith to derogate from prescription on a case by case basis (art. 7).

A brief introduction to the modifications made in the Normae de gravioribus delictis, reserved to the Congregation for the Doctrine of the Faith, given at the Congregation for the Doctrine of the Faith, 21 May 2010.

http://www.vatican.va/resources/resources_rel-modifiche_en.html