Coat slow cooker bowl with nonstick cooking spray. Place pears, apples, cherries and cranberries in slow cooker and mix together with sugar, cornstarch, vanilla and cinnamon until well blended. Cover and cook on HIGH for 30 minutes.
Meanwhile, mix together flour, oats, brown sugar and cinnamon. Cut in the butter with a pastry blender or fingers and mix until mixture resembles coarse crumbs. Lift lid and spread topping evenly over fruit.
Replace cover and cook on HIGH for 3 hours more or until fruit is very tender. Let cool for 10 minutes before serving. Serve with ice cream, if desired.