1984 is more appropriate for adolescents than for kids under tweens. If anyone has read the ending, the imagery in Room 101 is pretty graphic. There are also sexually suggestive imagery in the middle of the book.
The best dystopian book for kids that warns of authoritarianism would be Fahrenheit 451 and Animal Farm imo. The latter was my introduction to George Orwell by my teacher just before I entered adolescence.