Core apples and cut a strip of peel from the top of each. Place apples, top sides up, in a 4-quart slow cooker.
In a small bowl, combine dates, brown sugar, and cinnamon. Spoon mixture into the centers of the apples, tamping down with a narrow spatula. Pour apple juice around the apples, and top each apple with a piece of the butter.
Cover and cook on LOW for 5 hours. With a large spoon, transfer apples to dessert dishes. Spoon some of the liquid over the apples, and serve warm with a scoop of vanilla ice cream on the side.