Preheat oven to 350°F. Coat 10 2 1/2-inch muffin cups with cooking spray; set cups aside. In a medium bowl whisk together the flour, sugar, baking powder, baking soda, and salt; set aside. In another medium bowl whisk together the egg, buttermilk, and oil. Add the liquid ingredients to the dry ingredients and stir just to combine. Divide the batter between the 2 bowls. Add your favorite mix-ins to half of the batter, and your child's to the other half.
Spoon batter into prepared cups, filling each about 3/4 full. Bake for 20 minutes or until golden. Cool in cups on a wire rack for 5 minutes; remove from cups. Serve warm or cool.
If you don't have buttermilk, you can make it by adding 1 tablespoon lemon juice to 1 cup of milk; stir and let stand 5 minutes.