Mietje Coster was the youngest of the four children of Barend Coster and Betje van Coevorden. She was born in Rotterdam on 22 August 1918 and lived with her parents and unmarried brother Jacob at home in the Vlaggemanstraat 26a, where they came to live up from Februray 1936. Her sister Sara was already married in 1928 and lived elsewhere with her family, just as her sister Hendeline, who was marri…