Anne Fine: The Chicken Gave it to Me [2002] paperback

Andrew arrives at school with a book full of scratchy writing, telling Gemma, 'The chicken gave it to me.' Inside they find a story entitled, The True Story of Harrowing Farm, in which aliens chuck a group of chickens out of the cramped, dark barn they've been reared in, to fill it with the humans they like to grow to eat. Despite having been kept horribly confined by humans, the chicken cannot bear them to suffer the same fate. Reading the chicken's words, Andrew and Gemma start thinking about their food, asking Vinit about his vegetarian diet and finding their classmates have a huge range of ideas - mostly contradictory - about where their meat comes from. The chicken, bravely, steps into one of the aliens' spacecraft, returns to their planet and runs into a chat show host. Appearing on alien TV, the chicken is able to spread the word about the human farms and convinces the aliens to care for their humans better before eating them. The chicken returns to earth and smiles to hear, from the grass of the field, Andrew and Gemma making up songs about free range chickens.