Even though Caillou is a little boy, he has a big job - he's Rosie's big brother!

Caillou helps Mommy, Daddy and Grandma with his little sister Rosie, and learns that sometimes it's fun just to be a little boy, too. Caillou also learns about growing up, and finds out that growing up isn't just growing taller, but also learning new things. Later, when Sara looses a tooth, Caillou learns one more thing about growing up...the Tooth Fairy!