More than 200 calls were received by Childline in the week following the Manchester Arena attack.
Some children who contacted the NSPCC service in the wake of the May 22 atrocity told counsellors they never wanted to go to a concert or public event again.
Others said they were so upset they could not stop thinking about what had happened at the end of the Ariane Grande concert, could not stop crying and some were experiencing panic attacks and flashbacks or having trouble sleeping.
Many youngsters spoke about feeling unsafe and not wanting to leave the house.
Anna Krala, Childline service manager in Salford, said: "Young people who have been contacting us after the terrorist attack were expressing, obviously, they were fearful. They could not understand what had happened and why. They were very anxious about 'will this happen again'. They were scared and they were really concerned about their friends and colleagues and family.
"They had read an awful lot and seen an awful lot in the media and the press, so this added to the anxiety and the fears. There was also a lot of anger as well because of not understanding why this happened. So there was a lot of confusion at the time.
"For young people, we have to understand their world. It's very different than an adult world and it's really difficult for us to understand why these things happen.
"So for a young person sometimes they don't have anybody to talk or maybe to listen. It's important for them to know there is somewhere where they can express their feelings and feel confident that if they are scared they can say they are scared and if they are worried they can say it.
"And be confident to know that Childline is listening. We are essentially a listening service, we don't question. That's what we are here to do."
Asked for advice to parents on how to tackle the issue of terrorism with their children, she said: "It's a difficult subject and essentially keep it simple. Don't over emphasise and keep your explanations and responses in the child's language so that you know they will understand.
"If a young person wants to know more then sit with them and help them find out more in a way they can understand. The other essential really is to listen. Let them feel comfortable that you are going to give them the time to do that and if they want to talk to somebody else, help them do that.
"Sometimes it's difficult for young people to talk to people they know. We do have quite a lot of young people who come to us who have been directed here by parents."
She hailed the "overwhelming" response of local volunteers on the day after the attack.
"We were on shift here very early the morning after and I was overwhelmed with the amount of volunteers who had turned up that weren't supposed to be here," she said.
"It wasn't their shift but they came in offering extra support to respond to the young people and also to respond to each other as well because it was quite an emotional time, a very confusing time.
"But in some respects we expect that from our volunteers because they are so committed. It's fabulous the support system we have."
- Children and young people can contact Childline for free, confidential support and advice, 24 hours a day on 0800 1111 or at www.childline.org.uk.