What is the name of Charlie Brown's younger sister?

Charlie Brown’s younger sister is Sally Brown.

Sally is a fictional character created by Charles M. Schulz for Peanuts. Her arrival was announced in the strip in May 1959, when Charlie Brown learned that he had a baby sister. She was officially named Sally in June and made her first visual appearance on August 23, 1959. As she grows, Sally becomes one of the strip’s younger recurring characters and a distinctive source of comic misunderstandings.

Sally is sometimes confused with Lucy, but Lucy Van Pelt is Linus’s older sister, not Charlie Brown’s. Peppermint Patty and Marcie are also friends from a different part of the Peanuts cast. Sally’s relationship with her older brother is affectionate but frequently exasperated: she admires Charlie Brown while also questioning his advice and decisions.

Another defining part of Sally’s story is her persistent infatuation with Linus, whom she calls “My Sweet Babboo.” Her naïve wordplay, complaints about school, and tendency to misinterpret expressions give her a voice distinct from the older children. Cathy Steinberg first voiced Sally in the 1965 television special A Charlie Brown Christmas.