Charles's older brother Peter is played by Mark Lenard, probably best known for his role as Spock's father, Ambassador Sarek, in Star Trek (1966).
In two episodes, of Little House on the Prairie (1974), Charles Ingalls as a rascal and youngster, was very well acted out by Matthew Labyorteaux, debuting in Journey in the Spring: Part I (1976) and I Remember, I Remember (1978). Matthew Labyorteaux is best remembered as Albert Quinn Ingalls, that was later added to the show as a new family member.
During a flashback, a young Charles mentions his sister, Lydia. However, she never appears in the series, nor is she ever even mentioned other than in this episode. His other sister, Polly, appears briefly as a child in the season four episode "I Remember, I Remember", also in a flashback, but like Lydia, is never featured or mentioned again anywhere in the series run.
Hersha Parady appears briefly as Charles' sister-in-law, Eliza. She would return in season four as regular character Alice Garvey.
Caroline's youngest sister Eliza Quiner married Peter Ingalls and became the third Quiner to marry an Ingalls. Peter Ingalls was Charles Ingalls (Pa's) older brother.