The Arnolds had six children:
- Thomas (1852–1868);
- Trevenen William (1853–1872);
- Richard Penrose (1855–1908), an inspector of factories;[note 1]
- Lucy Charlotte (1858–1934), who married Frederick W. Whitridge of New York, whom she had met during Arnold's American lecture tour;
- Eleanore Mary Caroline (1861–1936) married (1) Hon. Armine Wodehouse (MP) in 1889, (2) William Mansfield, 1st Viscount Sandhurst, in 1909;
- Basil Francis (1866–1868).