The UN children's fund has called for the creation of safe zones in Somalia for about 1.5m children whose lives have been affected by conflict.
Unicef estimates 1.5m children are at risk
Persistent battles in the capital between insurgents and Ethiopian-backed government forces have created Africa's worst humanitarian crisis, the UN says.
"We have reports of both parties recruiting child soldiers," Unicef's Christian Balslev-Olesen told the BBC.
It is estimated that 60% of Mogadishu's residents have fled their homes.
Insecurity has cut off food supplies and access to clean water and medical assistance.
The BBC's East Africa correspondent Adam Mynott says outside the capital, Mogadishu, where families have sought shelter from the fighting, the situation is equally precarious.
Unicef's Ann Veneman said "an immediate cessation of the conflict" was necessary to enable humanitarian workers to access those in need.
"Safe zones must be created where children and families can find assistance and stability," she said in a statement.
She said that not only were the children malnourished and at a high risk of disease, but they were also suffering from exhaustion and emotional trauma.
A mother and her three children were among the latest casualties of the ongoing conflict in the capital, Mogadishu, killed in shelling on Tuesday.
Mr Balslev-Olesen, Unicef's representative in Somalia, suggested that the few schools open in Mogadishu could act as the "safe havens" as the conflict was intensifying.
"This is an escalation of the conflict that we have not seen in the past... we have reports of insurgents simply using children to plant roadside bombs and so on," he said.
The number of children in need of urgent humanitarian assistance are scattered all over Somalia, but mainly in the central south and in pockets close to Mogadishu on the road to Afgoy, Unicef says.
Last December, Ethiopia helped the transitional government end the Union of Islamic Courts' six-month rule over large parts of southern Somalia, but Mogadishu has been a battleground for insurgents hoping to oust the Ethiopians.
Ethiopia says it wants to withdraw its troops, but only when they are replaced by peacekeepers.
So far only 1,600 Ugandan peacekeepers have been sent to Somalia, of a planned 8,000-strong force.
Somalia has not had a functioning national government since 1991.