Frans de Munck was the son of Frans de Munck Sr., a son of a Belgian inland skipper. De Munck Sr. worked as a stoker at a gas company in Goes, Zeeland, where he met Johanna Maria Labeur, a widow from Kattendijke. She had two children from her first marriage, and the couple settled on the Westerstraat in Goes. De Munck Jr. later had a half-brother from his father's marriage to Labeur, Pieter de Munck, who was seven years younger. His biological mother is unknown.
