Hmm, good point. Yet, I'm not sure if the movie was clear on how long he'd been away. It could have been a year, or even just a few months. In a practical sense, they probably just didn't want to get new actors to play older children - especially if the difference is only a year or so.

On the other hand, it is a little strange that the children were in the same exact position as when he remembered leaving them. O_O