That's the way Animal Farm will appear to your students at first glance (and first read), and that's a good thing. It's a compelling read that moves quickly and has meaning regardless of whether or not readers understand the sophisticated lambasting of the leaders (and followers) of the Russian Revolution that's going on between the lines. 

Many of your students will be able to sit down and read it in less that 45 minutes, and if they can, they should. Then, as your class discussions and activities enlighten them with regard to some of the novel's deeper themes and symbols, they can revisit the material and revel at the complexity of what, at first glance, appeared to be a simple "fairy story."