She has met victims at Royal Manchester Children's Hospital, and the staff who worked tirelessly through the night in the aftermath of Monday's atrocity.
Twelve children under the age of 16 - among the 64 casualties - were taken to the hospital by ambulance following the terror attack.
Prime Minister Theresa May visited the hospital on Tuesday afternoon.
The Queen condemned the "wicked" attack during her visit.
She met scores of staff who had worked through the night, shaking hands and sharing words with many, before visiting a ward where four young girls who were injured in the concert blast are recovering.
The Queen told 14-year-old victim Evie Mills, from Harrogate, and her parents: "It's dreadful. Very wicked. To target that sort of thing."
Evie had got tickets to the concert as a birthday present.
The monarch told the youngster she thought Ariana Grande was a "very good singer", adding: "She sounds very, very good."
She told Evie's parents that "everyone is united" following the attack.
Millie Robson, 15, was wearing an Ariana Grande T-shirt as she met and shared words with the royal visitor.
The Queen asked Millie, who suffered injuries to her legs, if she had enjoyed the concert before the attack - prompting the teenager to reveal she had won two VIP passes and met the global superstar backstage.
The royal described the atrocity as "very alarming" and wished Millie, from County Durham, a speedy recovery.
"It's not something you expect at all," the Queen said to father David, who was waiting at the exit of the arena for Millie when the bomb exploded.
One of the young victims, 12-year-old Emily Murrell, was forced to miss the visit as she received surgery.
Mum Ruth, who was also hit with shrapnel and is still recovering in hospital, said her daughter would be incredibly disappointed but spoke to the monarch in her absence.
Amy Barlow, 12, from Helmshore, Lancashire, was another of the teenagers who met the Queen.
She was joined by mum Cathy - who said she had not left the hospital since the pair were caught up in the attack - and dad Grant.
The group discussed the incredible community response to the atrocity before the Queen departed.