It's a sharp rise from as recently as six months ago, the U.N. agency said, when 73% of the migration flow was male, and only one in 10 migrants was an accompanied child. Now most are women and children.
"The implications of this surge in the proportion of children and women on the move are enormous -- it means more are at risk at sea, especially now in the winter, and more need protection on land," UNICEF's special coordinator for the refugee and migrant crisis in Europe, Marie-Pierre Poirier, said in a press release.
Last month, one in every five people who drowned while trying to sail from Turkey to Greece was a child, according to the International Organization for Migration (IOM). They included 10 children -- among 24 migrants
-- who drowned last week when their boat capsized in the Mediterranean Sea.
Migrants making the journey are fleeing war, poverty and persecution in Syria, the Middle East and Africa for the relative safety of Europe. The passage between Turkey and Greece is a popular route, and many don't make it. Last year, the IOM said 3,811 people had drowned in the attempt.
And if they survive the journey, there are other risks on land, particularly for children.
As many as 10,000 unaccompanied migrant children who have traveled to Europe may be unaccounted for, according to a recent report from the European Union's police agency, Europol
. The agency warned that children were at greater risk of abuse and exploitation at the hands of people smugglers.
More refugees than ever
Although the demographics may be changing, the number of refugees willing to risk their lives trying to travel to Europe by sea is showing no signs of slowing down.
More than one million migrants entered Europe in 2015, according to the IOM. And in the first 28 days of this year alone, the agency estimates that more than 55,000 migrants and refugees crossed the Mediterranean to enter Europe. So far, 366 of these have been reported dead or missing.
UNICEF called on the international community to make protection of women and children migrants a priority, and said the best interests of each individual unaccompanied child should be examined before taking any action.
"Welfare, protection and health systems need to be strengthened at every step of the way so that children and women are not exploited or fall between the cracks," Poirier said.