The star spent time with youngsters at the Royal Manchester Children's Hospital in a surprise appearance ahead of a benefit concert on Sunday.
Following the singer's visit, the father of one of the injured said he had never seen his daughter so happy.
Suicide bomber Salman Abedi killed 22 people and injured dozens more at Grande's 22 May Manchester Arena gig.
Grande arrived back in the UK on Friday morning ahead of the One Love Manchester concert at Old Trafford cricket ground.
Stars including Justin Bieber, Katy Perry, Coldplay, Take That and Miley Cyrus will join her for the event which is raising funds for victims and their families.
Peter Mann, whose daughter Jaden was injured in the attack, wrote of Grande's hospital visit: "This means more to us than all the amazing things people have done this week.
"So happy she came I could burst. Never seen Jaden so happy; even cried again myself."
Another girl, 14-year-old Evie Mills, was visited by Grande who also spoke to nurses and staff during her time at the Manchester hospital.
Evie was one of the youngsters who met the Queen when she paid her respects on 25 May to those injured in the bombing.
Abedi blew himself up in the attack at Manchester Arena, but police have made a number of arrests as investigations continue.
Ten men, aged between 18 and 44, remain in custody on suspicion of terrorism offences in connection with the attack, police have said.
A 15-year-old boy, a 34-year-old woman, and four men have been released without charge.