Sientje de Boer was a daughter of Leendert de Boer en Elisabeth Cracau. She married on 30 August 1933 in Amsterdam to Hartog Walvis, son of Zacharias Walvis and Fijtje Posener.
City Archive of Amsterdam, archive card of Leendert de Boer, Elisabeth Cracau and Sientje de Boer.
In addition, a Jokos file (number 30863) on this family is at the Amsterdam Municipal Archive. Access is subject to authorization from the Stichting Joods Maatschappelijk Werk.