They had five children who survived birth, and Paul was the youngest, having four older brothers Arthur, Emil, Hugo, and Otto. Johanna Ehrenfest worked long hours in their shop and Paul was looked after at home by a nursemaid.
Sila ay may limang mga bata na nag-survived kapanganakan, at Paul ay ang bunsong, pagkakaroon ng apat na mga mas lumang mga kapatid na lalaki Arthur, Emil, Hugo, at Otto. Johanna Ehrenfest nagtrabaho mahabang oras sa kanilang mga tindahan at Paul pagkatapos ay tumingin sa tahanan sa pamamagitan ng isang yaya.