Trim the bottoms off of the mini Bundt cakes to create a flat surface. Pipe about a tablespoon of frosting on the bottom of each cake. Place the bottoms of two trimmed cakes together to make them into one larger, round cake.
With a piping bag, pipe frosting down the sides of the cakes. With an offset spatula flatten the frosting all over the sides to create a sticky surface.
Pour the sanding sugar onto a plate. Roll each frosted cake through the sanding sugar until evenly coated so that the pumpkin gets an orange color.
Cut each Tootsie Roll in half. With your hands, twist the Tootsie Roll halves to make them look like stems. Place one stem on top of each pumpkin.