This isn't true. Parents aren't able to grant consent to a minor to have sex with someone of legal age - it wouldn't really make sense for parents to be able to determine the lives of their children whne they are still minors. For that reason, this statement is false.
Social researchers usually report their methods of finding because probably to tell people where they got their information from which is the source, to make sure its correct and not some propaganda and also to help other social researchers to get new methods of finding research. There are many ways to find research, from people, books, and even the internet.