So most families don't care about their children? I don't think so.
"Ask yourself why this girl turned to staff at her school and not her parents."
There are many reasons why people don't tell their parents, it's not necessarily because the parents don't care or won't be supportative, and can even be down to mis-perceptions. Many children who are sadly abused or bullied don't tell their parents, and it's not because their parents are bad at all; and it does not mean the parents should not be told.
If a child is on a social services watch list of some kind then it may be appropriate not to tell the parents.
The parents are in the majority ones in the best place both emotionally, and most able to be there when their child needs them. Unless of course you think the majority of parents couldn't give a toss about the wellbeing of their loved one.