Along with the English and Spanish versions, there is now a French version of the minor consent form. Here are links to the PDFs:
As for when they're needed, here's a reminder, from the Ethics Handbook:
"Be sure to consider legal issues when dealing with minors (generally defined as anyone under the age of 18). An interview of a minor about a sensitive subject requires us to secure permission from at least one of the minor's parents (preferably both) or a legal guardian. Examples of sensitive subjects include cheating, sexual activity, involvement in gangs or crime, difficult family relationships, probation violation, out-of-wedlock pregnancy or parenthood, victims' sexual abuse and similar topics that could have legal ramifications or lead to embarrassment. An interview of a minor in a special custodial situation, such as foster care, juvenile detention, or holding facilities for illegal immigrants, requires the consent of the person who has custody of the minor. Utah also requires the consent of both the custodian of the juvenile facility and the minor's parent.
"An interview on a non-sensitive topic (normal childhood activities, sports, book, movies, trips to the zoo, baseball and the like) does not require consent. Generally however, any interview on school premises will require the permission of the school authorities.
"In cases where there is even a hint of doubt about whether to get consent, contact our legal team (look for LegalAlert in the NPR internal email address book)."