Update: Olivia Campbell, 15, was identified Tuesday as one of the victims of the Manchester terror attack. Her mother posted on Facebook, "RIP my darling precious gorgeous girl Olivia Campbell taken far far to soon go sing with the angels and keep smiling mummy loves you so much."

Some families are still looking for their children after Monday night's bombing at Ariana Grande's concert in Manchester, England. One mother, Charlotte Campbell, spoke to British TV about her daughter, Olivia.

"I'm heartbroken at the moment because I don't know where she is. I don't know if she's alive even yet," Campbell said, choking up.

Islamic State of Iraq and Syria (ISIS) is now claiming responsibility for the explosion that happened at the end of the concert in Manchester Arena. CBS News confirmed the identity of the suicide bomber as 23-year-old Salman Abedi. He was known to British authorities prior to the attack.

Thousands of young people scrambled to get away from the scene. Among the victims identified so far include teenager Georgina Callander and 8-year-old Saffie Roussos, the youngest-known victim. At least 22 people have died in Britain's worst terror attack since the 2005 transit attacks in London, and 59 others are wounded.

When Campbell first heard the news, she tried to get ahold of Olivia.

"Couldn't get hold of her. There was many phone calls, and phoned the police. They weren't really helpful at that time because it was so fresh," she said.

The worried mother said she's thinking through "every possible scenario" for what could have happened to Olivia.

"That she's just going to walk through this door any minute like she's not even known what's going on. That she's in a hospital somewhere wanting me but no one can get a hold of me because they don't know who she is – or that she's dead," Campbell said.

She said Olivia was at the concert with a friend from school, who is now in the hospital with his family.