Preheat the oven to 350°F (175°C) and grease a 9x13 inch baking pan with non-stick spray or parchment paper.

In a large mixing bowl, combine the cake mix, eggs, and vegetable oil using a spatula or electric mixer until a thick dough forms.

Gently fold 3/4 cup of the pastel milk chocolate candies into the dough by hand.

Transfer the dough to the prepared baking pan and press it into an even layer reaching all corners.

Distribute the remaining 1/4 cup of candies and the sprinkles across the surface, pressing them lightly into the dough.

Bake for 20 to 22 minutes, or until the edges are lightly browned and the center is just set.

Remove from the oven and allow the bars to cool completely in the pan to ensure proper structure before slicing into 24 squares.