Twelve children under the age of 16 were among the 59 casualties taken to hospital after the terror attack at Manchester Arena.
David Ratcliffe, medical director of the North West Ambulance Service, said 12 patients were taken by ambulance to the Royal Manchester Children's Hospital.
It is not known how many children were among walking wounded who went to hospitals.
In a statement read outside the Manchester Royal Infirmary, Jon Rouse, Chief Officer of Greater Manchester Health and Social Care Partnership, expressed "deep condolences" to the victims and their families.
He said: "It's been a terrible night and morning in terms of Greater Manchester. Although we have also seen some of the best aspects of Greater Manchester and the people who live there as well."
The condition of casualties in hospital was not confirmed and no details were given on the types of injuries sustained.
Mr Rouse said: "Clearly there are a number of individuals who have very, very serious injuries and are requiring intensive care and people who are going to be in hospital for a long time in terms of that treatment."
Mr Ratcliffe said: "We sent 60 vehicles to the site, along with highly specialised crews, highly specialised teams, that were able to stabilise patients at the scene and ensure that they received the right treatment at the scene before evacuation to hospital. We took 59 patients to local A&Es around the Greater Manchester area."
He said nine patients had been taken to the Manchester Royal Infirmary, six to Salford Royal Foundation Trust, six to the University Hospital of South Manchester, six to Stepping Hill, eight to Bolton hospital, seven to the Royal Oldham Hospital and five to North Manchester Hospital.
He said: "There were also a good number of walking wounded, which we obviously didn't transport."
Mr Rouse said: "We want to say from the perspective of the ambulance service, but also the rest of the NHS as well, how overwhelmed we've been by the offers of support we've received from other parts of the country.
"People have just not been able to do enough for us."