3. Chloë Moretz
Why Chloë Moretz? We never see teenage characters in the Star Wars films and Chloë Moretz is making a name for herself as one of Hollywood's best teenage actors with a considerable number of significant roles under her belt. So if an attempt is made to introduce a younger character (such as Han and Leia's daughter Jaina), Moretz should be the first choice. She's a very talented actress for her age and would be able to effectively portray a younger character thanks to her probably being able to connect with teenage characters more thanks to teenage life being a pretty universal experience. Which would allow her to bring some of her own life experience and emotions to the role more than an older actor could.
Who Could She Play? A capable but still slightly naïve Padawan whose idealism hinders her life as a Jedi.