A charity has trained its counsellors to help parents who fear their children are being radicalised.
The NSPCC said its existing support line could now advise parents worried about extremists grooming a child.
It said counsellors had been trained to spot warning signs such as children isolating themselves or "talking as if from a scripted speech".
Recent terror attacks "highlighted the growing problem of individuals being influenced by extremism", it added.
The charity said it had already started getting calls to its free, 24-hour helpline from people worried about the problem.
'I didn't see the signs'
Khadijah Kamara from Brighton says her son Ibrahim became radicalised. He was killed while fighting in Syria in September 2014.
"There were signs that you just don't think about. You ignore them until after it happens and then it's only when you think back that you realise," she says.
Khadijah says Ibrahim became "withdrawn" and would "look down on other Muslims, if they were not practising enough". He also spent a lot of time outside of the house and was difficult to contact.
"I didn't even know about the word radicalisation, it wasn't familiar. When he spoke about Syria, I said 'you are listening to someone' but he would just get angry. He was in denial that they were going to war."
The training for NSPCC counsellors explains how extremist recruiters "befriend vulnerable targets, feed them ideologies and - in the worst-case scenario - persuade them to commit terrorist attacks".
The charity said potential targets often had low self-esteem, were members of gangs, or were victims of bullying or discrimination.
Radicals tell them they can be "part of something special, and brainwash them into cutting themselves off from their friends and family", it added.
Signs which may "hint at a child being radicalised" include children:
- Isolating themselves from family and friends
- Talking as if from a scripted speech
- Showing increased levels of anger
- Becoming disrespectful and asking inappropriate questions.
'I felt like a traitor'
One teenage girl from east London described how she became drawn into long intense discussions on the internet which led her to want to run away to Syria.
"I saw so much violence that it seemed to lose its effect," she said. "Everything merged into one. I can't believe I'm saying that now.
"My primary reason to want to go to Syria was to join Islamic State. I believed this was the best way to be a good Muslim.
"I believed the West were responsible for the suffering of Muslims particularly in Gaza where innocent people and especially children were killed. I felt a traitor living in the West.
"It was easy to maintain this divide between my real life and my online life as no-one knew me in real life."
NSPCC chief executive Peter Wanless said: "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."
The charity is advising concerned parents to:
- Look out for any signs of radicalisation
- Talk to the child and encourage an open conversation - ask them why they are feeling a certain way or why they have certain views
- Contact the NSPCC for further advice
- If a child is in immediate danger call the police on 999
The helpline number is 0808 800 5000 and callers can remain anonymous.