Have read up a bit more about this case and it certainly seems to be an act of family annihilation, very rare in women. I think Beyond has it perfect.
And there are clear similarities with the Turpin family too, with one of the children escaping to a neighbour's house in the middle of the night to ask for help and another child asking the same neighbour for food all non perishable - the child even asked that the neighbour not inform his parents - an immediate red flag for safeguarding.
The CPS were alerted when the neighbour's father rang the police; his daughter felt very uneasy about it and told her dad as her husband had said not to get involved. To be fair the CPS did act quickly but by then it was too late - they all left and then were murdered by the driver at the wheel.
The picture I was looking at was not where they had gone off the cliff. Just shows you have to be accurate before you post!