Whisk together flour, cake mix, sugar, baking powder, baking soda, and salt in a large bowl. In a second bowl, whisk together eggs, buttermilk, milk, melted butter, and vanilla. Add to dry ingredients and whisk just to combine. Fold in sprinkles.
Heat griddle to 325º-350ºF and spray with non-stick cooking spray or butter, if desired.
Scoop 1/3 cup portions of the batter onto prepared griddle, leaving space between them. Cook until bubbles start to form and bottom side is golden brown. Flip and cook until remaining side is golden brown. Remove to a plate and cover until ready to serve. Repeat with remaining batter.
If desired, top pancakes with this glaze: Mix together 1 cup powdered sugar, 1 teaspoon vanilla, 3-4 tablespoons milk. And don't forget a sparkler!