Matilda “Mattie” Gladwaller is the young daughter of John Gladwaller and his (unnamed) wife and is sister of Babe Gladwaller. She was likely born in 1933, judging by her age when her brother is sent to serve in France. Mattie is very close to her brother and writes to him during the war. After he returns, Mattie and Babe visit Helen Beebers to tell her about the death of their mutual friend, Vincent Caulfield.
Mattie appears in all three of Babe Gladwaller’s stories, Last Day of the Last Furlough, A Boy in France, and The Stranger. Like Phoebe or Sibyl, Mattie reminds Babe of innocence and serves as a counterpoint to the situations he finds himself in. Like most Salinger children, she also has some Teddy in her, a wise child.
Trivia
Mattie is said to be 10 in Last Day of the Last Furlough, which seems to take place in November, 1943