So far this year, around 4,000 people have made the treacherous crossing to Europe via the so-called Central Mediterranean Route from North Africa to Italy - nearly 80 per cent less than in the first seven months of last year.
On Sunday, more than 400 people were rescued off the Libyan coast by two boats at the centre of UNICEF's appeal.
One of the boats, Open Arms, is reportedly moored close to the Italian island of Lampedusa.
UNICEF said that only 11 of the 103 children aboard the second vessel, Viking Ocean, had a parent or guardian with them.
In a statement, UNICEF Special Coordinator for the Refugee and Migrant response in Europe, Afshan Khan, said that many of the youngsters had fled poverty, conflict and unthinkable atrocities, and had the right to be safe.
Amid reports that the Spanish authorities had agreed to shelter more than a dozen of those rescued at the weekend, many of whom are from Sudan, Ms. Khan welcomed what she called recent progress towards a plan for increased solidarity and responsibility sharing among European Governments.