It is one of the most striking things that makes life in the premodern past so unimaginably different from today. To be a parent was to suffer continuous tragedy. An example: Queen Anne of Great Britain (1665-1714). She was pregnant 18 times, and not one of her pregnancies resulted in an adult child to inherit her throne. Miscarriages, stillbirths, and five children born alive. Four died in infancy from various causes. One, Prince William Duke of Gloucester, lived to age 11, when he died of an infectious disease - probably smallpox. His death was one of the key events that led to the House of Hannover (the current British royal family) inheriting the throne in 1714.

Smallpox probably killed about a billion people, many of them children, before its eradication in the 1970s due to a global vaccination campaign. You can see it is listed in the Bills of Mortality in TFA, always with a high number of deaths.