It has to be at least in the ballpark of plausibility, yes. Acting and presence, of course, are a big deal. But you do actually have to take into account what the actors playing the parents look like. A few stats: Natalie Portman - 5'3" Hayden Christiansen - 6'2" Harrison Ford - 6'1" (peak height before a lot of back surgery after Temple of Doom), age 70 (character age started out 4-5 years younger than him at 29--he was 33 when filming started in March 1976) Carrie Fisher - 5'1", age 56 (character age started out the same age as her at 19) Mark Hamill - 5'7", age 61 (character age started out 5 years younger than him at 19--he was 24 during filming) Mark is likely going to get dwarfed by any male actor chosen to play Han and Leia's male offspring (LOL) in any Jedi training sequences (particularly if they're aiming to not make the male offspring look like a puny weakling next to Harrison--see Shia). As I mentioned repeatedly in the Mara Jade casting discussion, age and height are factors (don't go too young or too statuesque). Obviously, the only people that are going to be shorter than Carrie are little people actors. Nina Dobrev is 5'6" and 23, by the way.