These crops are then fed to our cattle, which are then killed for meat. As a result, local people may go hungry, especially when the crops fail. This initial questioning may throw up lots of other issues and questions. The children may have seen news stories about the difficulties of farmers who cannot sell their livestock, the reporting of BSE and other health scares, or animal rights activists demonstrating against live exports. Try to keep the discussion focused on meat vs. vegetarianism.
Animal rights are a massive topic.
Draw a line down the middle of your blackboard showing reasons for and against vegetarianism. These things cannot be proved scientifically. Try to focus on the present day. You may have veggies and meaties in your class. Explain that it is a good thing to have a broad range of views in society - variety is the spice of life.