Our children are living in a world in which the offline and online are one and the same. So giving them the information, power and resilience skills they need to survive the pitfalls and make the most of the positives is an essential part of every childhood.

I have spent the last few years calling on government, schools and parents to do more to make sure children can avoid the pitfalls – and just as long calling on the social media companies to take more responsibility for the content they host and the design of their platforms.

The tragic suicide of Molly Russell and her father’s appalled response to the material she was viewing on social media before her death have again highlighted the horrific amount of disturbing content being accessed by children online. It should be a moment of reflection for the tech companies, and an opportunity for them to accept there are problems and commit themselves to tackling them.

Nobody, including the social media companies themselves, could have predicted a decade or more ago the impact they would have on the lives of children and young people. Some of that impact can be positive and beneficial. But when things go wrong, parents and children have a right to know that protections are in place and that there are easy to access means of redress or easily removing content. Yet too often, the internet giants seem remote, unwilling to be transparent and slow to take responsibility for what is hosted on their platforms.

In my report Growing Up Digital, I called for the establishment of a Digital Ombudsman, financed by the internet companies themselves, but independent of them. It would be an arbiter, able to respond to the concerns of children and parents by demanding greater transparency and action from internet companies so material that is detrimental to the wellbeing of children is removed quickly.

I am more convinced than ever that this is needed now and that the time has come for real action from this multi-billion dollar industry. Today I have written to Facebook, Instagram, YouTube, Pinterest and Snapchat calling for them to step up to the plate and to agree to be bound by a statutory duty of care, a legal obligation to prioritise the safety and wellbeing of children using their platforms, and to sign up to the idea an independent ombudsman.

These companies have great power over our lives and the lives of our children. With great power comes great responsibility, and it is their responsibility to support measures that give children the information and tools they need growing up in this digital world – or to admit that they cannot control what anyone sees on their platforms.

Anne Longfield is the Children’s Commissioner for England