This child never existed. He is an invention of historian James Hamilton Wylie based on a misreading of Bolingbroke's account books from 1382, in which Bolingbroke is recorded as gifting a messenger with a few pounds for reporting good news on the birth of a boy. Wylie read this to mean that Mary had born a boy. Nearly a century later, K.B. McFarlane repeated Wylie's findings in his own history of the Lancastrian kings, apparently without investigating the matter further. More recently, Alison Weir included the boy in her royal genealogy book -- she even gives him the name Edward and claims he lived for just four days, pieces of information that appear nowhere else and for which she provides no source.
Historians like Ian Mortimer, Kathryn Warner and others have thoroughly debunked the existence of this boy, based on two pieces of information that Wylie missed: Firstly, the messenger to whom Bolingbroke gifted money for having delivered good news was in the employ of the duke of Gloucester, suggesting that the messenger was announcing the birth of Gloucester's son, Humphrey, who was born in 1381 or 1382. Secondly, Bolingbroke's account books don't put him at the same place as Mary after their marriage -- Mary instead appears in the books of her mother's household. That is to say, the two lived apart ... so how could the child be conceived?