Preheat the oven to 375 degrees Fahrenheit.
Place fruit in a 9x13 pan. (Or 8x8 if you’d rather it have thicker fruit and crumble)
In a small bowl, mix together rolled oats, brown sugar, flour, butter and cinnamon using a pastry cutter or your fingertips. This is a great step to let kids of any age help with! Let them get their fingers in there, squishing and mixing the crumble ingredients.
Sprinkle the mixture evenly over the fruit.
Pat down lightly (optional).
Bake for 30-40 minutes or until fruit is tender and crumb topping is browned.