The three children are told lies of various degrees. Living totally isolated from the world and in a manufactured universe, they do not react like normal people would. The lack of awareness and exposure makes for very interesting scenarios and reactions.
The film can be pondered upon on several levels. For instance, governments never really tell their people any thing close to the whole truth. Thoughts on these lines - the harms caused by leaving people in the dark are the obvious things one can take back from the movie.
I am very interested in the alternate viewpoint of the parents though. They genuinely thought exposing the children to the world would be harmful for them. While that is not some thing one can possibly agree with, there are some positives which do come out of it in my opinion. For instance, when one of the girls who has never having been exposed to popular culture, dances (see video on youtube here), she creates some thing unique. As she has not seen any thing before, she is not influences by any thing and creates her own style. That is a positive in my mind.
This is film which is close to a masterpiece. When the film had released, it was panned in The New York Times and received an average review from Roger Ebert. I am quite pleased then, that it is slowly getting appreciation and is ending up in a few best of the year lists as well. This is a must watch according to me. 8.5/10.