Robert Emden married Klara Schwarzschild, the sister of German physicist and astronomer Karl Schwarzschild and the aunt of the German-American astrophysicist Martin Schwarzschild. They had six children of whom the names of five are known: Charlotte Schein; Emma Müller; Antonia Flach; Karl Emden, and Johanna Luise Berchtold-Emden. Although he married into a strongly scientific family, Robert Emden's children are not noted for any contributions to science.