Lewis Carroll was one of eleven children in his family, including himself.
Born Charles Lutwidge Dodgson in 1832, Carroll was the third-oldest of the eleven children of Charles Dodgson, an Anglican clergyman, and Frances Jane Lutwidge. The family lived in a strongly religious, northern English household and later moved to Croft-on-Tees in Yorkshire, where they remained for about twenty-five years.
Carroll was the oldest boy, though not the oldest child. His siblings included several brothers and sisters, and a number of them later became notable in their own right. His brother Edwin was a clergyman, while his sister Elizabeth helped preserve family memories and papers.
The number eleven can be confused with the ten-member hunting party in The Hunting of the Snark, another Carroll work. It also does not refer only to the children who survived infancy or to the siblings who reached adulthood; the standard biographical count describes Carroll as the third oldest of eleven children. Thus “eleven” is the accepted answer when the question includes Carroll himself.