They are a complex term that involves rights and duties. Parental rights are defined as the right and duty to protect, nurture and educate. Note the operative words, right and duty. If you don't fulfill your duties, or are suspect of not being able or willing to fulfill them, you lose some of these rights or somebody is appointed to represent the minor. This was not invented recently.
Lets start with the origin of the concept in western law.
The most useful antecedent in western legal thought is roman Law. This authority, so severe in the letter of the law but not used in practice, was mitigated by the Romans fine juridical instincts. The advent of Christianity softened the institutions. This disposition towards kindness is what makes parents sacrifice for the sake of their children. It is very clear that kindness implies that duties are involved.