As a child, Sammy would always play with Charlotte, showing that he has a fun personality
Five Night at Freddy's Novel Series
The Silver Eyes
According to the novel, Charlie is the daughter of Henry and Sammy's twin sister
On Halloween, 1982, Afton donned the Spring Bonnie suit, and he kidnapped and murdered Sammy, Charlie's twin brother, when they were both toddlers. While William was suspected of committing this murder, he wasn't charged; as a result, the diner ends up closing down.
In 1993, Charlie, Jessica, John, and Carlton return to the restaurant, accompanied by their friends Lamar, Marla, and her 11-year-old brother Jason.
They discover the still-functioning control panel which makes the robots move, and Charlie finds a fourth robot - Foxy the Pirate Fox - which cuts her arm with his hook. The next morning, haunted by recent events, Charlie tells John that before moving to Hurricane her father owned another restaurant called Fredbear's Family Diner, which featured two performing robots, yellow versions of Freddy Fazbear and Bonnie the Bunny.
John drives Charlie to the abandoned diner in New Harmony, and she remembers the day her brother Sammy was abducted by someone in a Bonnie costume, which led to the diner going out of business and Charlie's parents divorcing. She suspects that Sammy's abduction and Michael's murder are connected.
Charlie and John go to a library to research the history of Fredbear's Family Diner, and find an old newspaper article about Sammy's kidnapping with a photograph of Dave, who the newspaper identifies as the diner's co-owner.
The Twisted Ones
In the The Twisted Ones, He appears as a ghost that only Charlotte can see. He also appears in her nightmares.