The NSPCC has trained its counsellors to spot signs of youngsters being radicalised after receiving calls from parents concerned about their children.
The children's charity said adults could now ring its existing support line to be given advice should they fear their child might be at risk of grooming by extremists.
It said staff had been told how to look out for warning signs, which include youngsters isolating themselves or "talking as if from a scripted speech".
Peter Wanless, NSPCC chief executive, said recent terrorist attacks highlighted the growing problem of individuals being influenced by extremism.
He said: "It is vital that we are here for parents when they need our support and are able to provide them with non-judgemental advice on issues ranging from the wider terrorist threat to the dangers of radicalisation.
"Of course, the fact that a young person might hold extreme or radical views is not a safeguarding issue in itself. But when young people are groomed for extremist purposes and encouraged to commit acts that could hurt themselves or others, then it becomes abuse. That's why we've trained our helpline practitioners to cope with this fresh danger to young people."
The NSPCC said children at particular risk may have low self-esteem, be members of gangs or a victim of bullying or discrimination.
Experts in extremism have given NSPCC staff training on how recruiters "might befriend vulnerable young people, feed them ideologies and – in the worst case scenario – persuade them to commit terrorist attacks".
It comes after IBTimes UK reported last month on a mosque in Luton which had begun giving children as young as 11 classes to prevent them being radicalised by violent Islamic State (IS, Daesh) jihadists.
Imams and Islamic teachers in the UK had warned a war of ideologies is currently being fought in their own mosques, communities, and on social media following the rise of terror groups in Syria and Iraq.
Minister of Security Ben Wallace said: "We have seen all too tragically the devastating impact radicalisation and terrorism can have on individuals, families and communities. Protecting those who are vulnerable is a job for all of us. That's why we have provided the NSPCC with financial support which has paid for additional counsellors and expert training.
"We would encourage anybody who is worried that they or somebody else may be vulnerable to radicalisation to call the NSPCC and seek their completely confidential advice."