Preheat oven to 375°F. Grease a 2-quart baking dish.
In a bowl, toss together apples, peaches, and sugar. Pour into baking dish.
In another bowl, combine oats, brown sugar, flour, and cinnamon. Cut in butter until mixture is crumbly. Mix in walnuts. Sprinkle over fruit. Bake for 30 minutes, or until fruit is tender and topping is golden. Serve warm.