William and Elizabeth had seven children, three daughters and four sons. The first son, Thomas Jeffery Parker, became Professor of Zoology and Comparative Anatomy in the University of Otago, New Zealand; the second, William Newton Parker, became Professor of Biology in the University College, Cardiff; the third was a draughtsman and lithographer; the fourth was a surgeon. In his work on the vertebrate skull Parker became close to Thomas Henry Huxley, and named one of his sons after him. His first son was sent to study under Huxley, and became in 1872 one of Huxley's demonstrators.