But despite the school, the County Council and the police all being aware of concerns over the relationship prior to their disappearance, Megan’s parents were not informed of the situation.The school knew, the police knew - and as the article says, they knew for 7 months. And they chose to not inform the parents.
They considered that their sovereign right - to decide what was in the girl's best interests, and they exercised that (supposed) right by deciding not to inform her parents.
When the secular state, as it inevitably must, awards itself god-like powers, then that equally inevitably means the erosion of parental powers.
Only a Christian world-view can with logical consistency allow for a separation of powers on earth and family sovereignty. Because the ultimate ruler is in heaven, he can apportion out powers to different actors underneath him as he sees fit. The Bible reveals that he has delegated certain powers to the family, certain to church, and certain to the state. Neither is free to encroach on the other's territory. The question of "should we tell the parents that she's in a relationship with the maths teacher?" cannot arise. There is no right for the state to withhold such information. Jesus has not permitted it. The ultimate rule of daughters belongs to parents, not to the state.
But when the heavenly power is subjected to (would-be) abolishment, divine power passes inevitably (however slow the process) to the state. The state then, as the all-sovereign supreme being, decides who to delegate its unlimited powers to. If it decides to not allows the parents to know what the daughter is doing with one of the state's employees, then that is that. There's no final court of appeal, since we're such an enlightened people as to have religion out of politics and left no higher powers or divinely bestowed rights from our creator to invoke.