Casting Emily Browning as the younger sister is a mistake and I feel that they are missing a trick.
A much better casting decision would have Browning as the elder of the two sisters and Miranda Cosgrove, from The School of Rock, as the younger.

Miranda Cosgrove
Although, as I mentioned earlier, I will be interested in seeing how Browning performs, I think that she has a really good career ahead of her, she is very talented.
Anyone in doubt should watch her in Lemony Snicket's A Series of Unfortunate Events, without doing very much she constantly steals the screen, and the film itself is actually pretty good, don't believe the haters.