A three-year-old refugee boy drowned early Saturday near the Greek island of Chios after the engine of the boat his group was sailing in exploded, the Greek coastguard said.
The explosion threw the boat occupants into the water as it lay immobilised in shallows east of the island, the coastguard said.
Fifteen other people were rescued, including two that required hospitalisation, it said.
An 18-year-old was arrested as a suspected trafficker.
Greece has been overwhelmed this year by a migration crisis unseen in Europe since World War II.
The United Nations on Friday said over 800,000 people have crossed the Mediterranean to Europe this year, with over 3,400 dying in the process.