Green’s Dictionary of Slang

an illegitimate child.

1909		J. Ware Passing Eng. of the Victorian Era 2/1: Accident. A child born out of wedlock.
1932		D.L. Sayers Have his Carcase 322: Jenny Moggeridge’s Baby Charles what was a accident what Mrs Moggeridge was looking after.
1999		Rebirthing N.Z. 🌐 Many children are unwanted, unplanned, ‘accidents’, or illegitimate.