Tom Blackett was a 3-year-old brother to the Amazons, at one time considered by Arthur Ransome as a character in Swallows and Amazons. The little chap did not survive the rewriting of the book before publication. A draft list of the characters including Blackett family children was on p31 and 32 of Roger Wardale's book "in search of Swallows & Amazons" (and in CFT p22):
Amazons: Jane 13, Mary (proper name Ruth) 12, Tom 3.
Parents to Amazons: Smith (scored out) Walker.
Amazons: Jane (scored out) Nancy 13, Mary (scored out) Peggy 12, Tom 3.
It can be seen that the Amazons would have had two parents (perhaps called Walker) while perhaps the Swallows would have been fatherless.