UN officials and truce monitors in Sri Lanka say those killed in a bombing raid in a rebel-held northern area were pupils from local schools.
About 100 children are being treated in hospital, Unicef says.
The target of the air strike has been described by the government as a rebel camp and by the rebels as an orphanage.
Tamil Tigers rebels say 61 children died and hundreds were wounded.
The strike took place in Mullaitivu district on Monday. Teams from the UN children's fund (Unicef) and truce monitors went there the same day.
Unicef and Sri Lanka Monitoring Mission officials who visited the site said the victims came from local schools.
Unicef spokeswoman Joanna Van Gerpen told the BBC: "We did see more than 100 [wounded] in the local hospitals, some with loss of limbs, head and shrapnel injuries."
She said most of those injured were girls aged 16 to 19, and there was no evidence that any were rebels.
Ms Van Gerpen added: "From what we understand at this point, these children were from surrounding communities."
She could not confirm how many people had died in the raid.
A spokesman for the Sri Lanka Monitoring Mission (SLMM) - which also visited the area - said no sign of rebel activity had been recovered from the site.
The government says the bombed facility was a training camp run by the Liberation Tigers of Tamil Eelam (LTTE) and those killed were child soldiers.
'No war experience'
On Tuesday Sri Lankan government spokesman Keheliya Rambukwella said neither team had used military experts to reach their conclusions.
"They have not sent people with any war experience to study the place," Mr Rambukwella told reporters in Colombo.
"We have studied this for three years and know what was going on. They used this place to provide combatants to the Tigers."
Meanwhile, fighting has been continuing between troops and rebels in the northern Jaffna peninsula.
The government has also been carrying out a huge search operation, saying the rebels have moved into civilian districts.
The military said it was using the air force against rebel positions
It says it fears reprisal attacks after Monday's violence.
Schools have been closed early for holidays after a bomb exploded near the Pakistani high commissioner's car in the capital, Colombo, on Monday, killing seven people.
The Tigers have ruled out peace talks with the government while heavy fighting continues between the two sides.
The recent flare-up in fighting has prompted international alarm that a 2002 ceasefire agreement is unravelling.
The truce aimed to halt more than two decades of war between the government and the rebels, who want an independent homeland for minority Tamils in the north and east.
It remains officially in effect, despite months of violence.