Preheat oven to 350 F. Line a 15 x 11-inch pan with foil: set aside. In a small bowl, mix graham cracker crumbs, butter and 1/4 cup sugar until well combined. Spread mixture into prepared pan. Using a measuring cup with a flat bottom, smooth mixture to form an even crust. Bake crust until fragrant about 6 minutes: let cool completely. In a medium bowl, combine flour, cinnamon, baking powder. baking soda and salt. In a separate bowl, beat eggs, remaining sugar, pumpkin puree and oil; stir in flour mixture. Using a rubber spatula spread the pumpkin mixture evenly over the cooled crust in pan. Bake until filling pulls away from the pan, 25-30 minutes: let cool completely in pan. Frost the top of the cooled bars with cream cheese frosting. Gently drag the tines of a fork from side-to-side through the frosting to create a wave pattern. Sprinkle with Halloween-shaped sprinkles.