Brigitte, age 15, is played by a 23-year-old Emily Perkins. Katharine Isabelle, who plays her big sis Ginger, is four years younger than Perkins. What's really weird is that the characters actually look their age, right down to Brigitte appearing younger than Ginger.
Ghost in the second film. Tatiana Maslany was 19 at the time of filming, but Ghost is 13.