The January 2016 issue of The Psychologist, the flagship magazine of the British Psychological Society, includes a piece on the history of stereotypes surrounding only children. In “Screwed up, little despots?” Alice Violett notes
Negative perceptions of only children can be traced back to at least 1850 in Britain, and writers who identified themselves as psychologists expressed concerns about only children as early as 1867. Tellingly, the unprecedented concern with only children coincided with an increase in only children in middle-class families, which caused alarm among eugenicists. The increasing popularity of Darwin’s ideas about the importance of environment (as opposed to inborn ‘goodness’ or ‘badness’) in determining human behaviour, may also have had an impact. The only child’s problems were believed to originate in the home, where they supposedly experienced too much adult company and not enough contact with other children. Not unexpectedly, one of the results of the former was said to be the over-indulgence and over-valuation of only children.
The full piece can be read online here.