Rosie (known in French as Mousseline) is one of the main characters in Caillou who's the titular character's two-year-old baby sister. She is also the daughter of Boris and Doris and the granddaughter of Grandma and Grandpa. She was shown as a newborn in Big Brother Caillou. When she first met Caillou, he did not like her and was mean to her, but had warmed up and treated her nicely later. She is voiced by Brigid Tierney in the first two seasons, then Jesse Vinet.