Sprog is a British aspersion for a child, akin to the American term "runt", "ankle biter" or "rug rat". Sprog in all likelihood comes from the term "sprag" which refers to a young salmon. In the 18th century, sprag came to refer to a gay, cheery youth.

By World War II, "sprog" had entered into the British army's slang lexicon and was used in a derogatory sense to refer to a new recruit or someone in the lower ranks. After the war, former soldiers started making lots and lots and lots of babies and sprog, being too good a word to forget, got applied to children.