Police say they have detained the parents of the baby boy for questioning.
According to police, the parents had gone for a stroll on Monday, a French holiday, and left the 18-month-old with his three-year-old sister in the family apartment in eastern Paris.
Police said Tuesday the little boy somehow had access to an open window and fell out. He hit an awning of a ground-floor restaurant then bounced into the arms of a passer-by.
They said no injuries were uncovered by initial medical exams.