They were among 120 people who were deliberately pushed from a boat into the sea by the smuggler who apparently feared arrest.
Some 27 survivors were found on a beach by the International Organization for Migration (IOM) on a routine patrol.
Twenty-two are missing while the rest have moved on, the IOM said.
It added in a statement that the average age of the Somali and Ethiopian passengers on the boat appeared to have been 16. They had been hoping to reach countries in the Gulf via war-torn Yemen.
"The survivors told our colleagues on the beach that the smuggler pushed them to the sea, when he saw some 'authority types' near the coast," explained Laurent de Boeck, the IOM Yemen Chief of Mission.
The smuggler has already returned to Somalia to pick up more migrants to bring them to Yemen on the same route, they told the IOM.
"This is shocking and inhumane," Mr de Boeck said. "The suffering of migrants on this migration route is enormous. Too many young people pay smugglers with the false hope of a better future."
Despite conflict and a dire humanitarian situation, Yemen is still seen by many Africans as a gateway to the rich Gulf states or Europe, and thousands make their way there every year in crowded boats.
Around 55,000 migrants have left the Horn of Africa to come to Yemen so far this year, more than half of them under the age of 18 and a third thought to be female, the IOM estimates.
Many others also try to reach Europe via Libya and the Mediterranean Sea.
A note on terminology: The BBC uses the term migrant to refer to all people on the move who have yet to complete the legal process of claiming asylum. This group includes people fleeing war-torn countries such as Syria, who are likely to be granted refugee status, as well as people who are seeking jobs and better lives, who governments are likely to rule are economic migrants.
At least 29 teenage migrants were deliberately drowned by a people smuggler in Yemen, the UN's migration agency says.