The 91-year-old monarch spoke with medical staff and victims of the attack.
She thanked hospital staff for their hard work in caring for those injured.
Twelve children under the age of 16 were taken to hospital following the explosion at the Manchester Arena, which was detonated by Salman Adebi as fans left an Ariana Grande concert.
Of the 64 casualties, five children remain in critical care.
The Queen told Evie Mills, 14, and her parents: “It’s dreadful. Very wicked, to target that sort of thing.”
Evie, from Harrogate, said she was given tickets to the show as a birthday present.
The monarch told the teenager she thought Ariana Grande was a “very good singer”, adding: “She sounds very, very good.”
The Queen told Evie’s parents that “everyone is united” following the attack.
The Royal also spent time at the bedside of Millie Robson, 15, from County Durham, who was injured in the attack.
Millie, who was wearing an Ariana Grande T-shirt when she met the Queen, was in the foyer when the bomb struck.
Millie said she had won two VIP passes for the concert and had met the popstar before the show began.
The Queen said the atrocity was “very alarming” and wished Millie a speedy recovery.
She told Millie’s father David, who was by his child’s bedside: “It’s not something you expect at all.”
A minute’s silence was held at 11am on Thursday, with hundreds of people gathering in St Ann’s Square, in Manchester. to pay their respects.
After the minute’s silence for the victims of the attack, the crowd broke into a rendition of Oasis’s hit Don’t Look Back In Anger.
Ripples of acknowledgement travelled through the crowd before many others joined in in great gusto.
The song was a hit for the Manchester-based band headed by Liam and Noel Gallagher in 1995.