The Lufthansa flight was en route from Frankfurt to JFK airport in New York when it declared a medical emergency and landed at Shannon Airport in the southwest of the country.
The passengers were taken off the plane to be interviewed by Gardai (Irish police) in an effort to establish how the child died.
A police spokesman said the flight had originated in Addis Ababa and had arrived in Ireland via Germany but he refused to comment on reports that the child was Ethiopian.
"We always have to make the necessary inquiries to ensure there was nothing suspicious about the death. We are still trying to establish what the circumstances are," the spokesman said.