Transcript for Manchester suicide bomber cruelly targeted the most vulnerable

The awful reality. This attack, where so many young people would die. The mother who is still missing. Reporter: From the teenagers who were on their own for a concert, to the children running out holding their mother's hands. The attack was cruelly aimed at young lives, innocent children. Among the dead, saffie Roussos, just 8 years old, separated from her mother and big sister. She did not survive. Her school saying today, "She was simply a beautiful little girl loved by everyone." There are reports here her mother was critically injured, in the hospital, and might not be aware of what happened to saffie. 18-year-old Georgina Callander had her picture taken with the pop star two years ago and was back to see her in concert. She did not make it out. And at a vigil here in Manchester, a town square filled with thousands to honor the young faces who did not get out. It's a horrible thing that's happened. It won't change this city. Reporter: Why was it so important for you to come out today? It's an attack on Manchester, which is our city. I think everyone needs to show support and so that we are all together and we are all strong. I cannot begin to imagine what the parents are going through. Anyone who's a mother, like myself, you just cannot bear too much. Reporter: And the children who are struggling for words. What should everyone do now? Um -- carry on as we usually do. Just not hurt anyone or feel angry at anyone. Reporter: Tonight, more than a dozen still missing. Families and friends still waiting, searching. I'm sharing pictures of missing people. People that need help. Reporter: Looking in hotels, side streets, hospitals. A teenager's uncle searching for his 15-year-old nice, Olivia. You haven't seen this girl by any chance, have you? Excuse me, I'm just asking if you've seen this young girl. Reporter: Olivia's mother, Charlotte, holding a picture of her daughter. If anybody has seen her, please contact the police. Contact somebody. Let you know you've seen her. Just let the police know, please. Reporter: A desperate plea from a mother. Please just phone me and come home please. Reporter: The #missingmanchester has been shared around the world. Chloe Rutherford and Liam curry, missing. Laura Macintyre and eilidh Macleod, still not found. Courtney Boyle and her boyfriend Philip tron. Martyn Hett, separated from his friends at the end of the show. And this mother, Wendy Fawell, who hasn't been seen since the concert. But there are families tonight, thankful and relieved, posting photos of the missing they've discovered alive. And this tweet -- "All of these people have been found. Let's keep going." And here in this square, we met a grandfather whose own wife is a child psychologist and first responder. She's been helping children and hasn't been home yet. It's cowards and it's the weakest. Affecting people that are the weakest and families that are affected. And I don't know what they hoped to achieve. The grandfather and his wife counselling the youngest

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