In a food processor with a blade attachment, mix both flours and 1/2 cup butter. Process until butter is the size of tiny peas. Add water; pulse until dough pulls together. Let your kid form it into a 5-inch disk on a floured surface. Cover; refrigerate for an hour.
Preheat oven to 425ºF. Prepare a floured surface. Ask your child to roll the dough into a 12-inch circle about 1/8-inch thick. Help him check the size with a ruler. Put the dough on a baking sheet lined with parchment paper.
Quarter apples; slice 1/4-inch thick. Ask your kid to mix apples with the cranberries, sugar, and cinnamon and spoon into center of dough, leaving a 2-inch border. Fold dough over and dot center with remaining butter. Bake 35 minutes, until crust is golden and fruit bubbles.