Preheat oven to 350ºF and lightly butter an 8 X 8 inch baking dish.

In a medium mixing bowl, whisk together the flour, oats, baking soda, and salt until well combined. In the bowl of a stand mixer fit with a paddle attachment, beat the brown sugar and butter together on medium speed until light and fluffy, about 3 minutes. Add vanilla extract and continue to beat another few seconds.

Turn off the mixer and scrape down the bowl. Turn mixer on low speed and add half the dry ingredients, mixing for a few seconds, just until combined. Add the milk and mix until combined, then add the last half of the dry ingredients and mix just until a stiff dough forms. Remove the bowl from the stand mixer and fold in the butterscotch and chocolate chips with a rubber spatula.

Scoop the dough into the prepared baking pan and use a spatula or your hands to spread it evenly in the pan. Press the candy pieces and candy eyeballs lightly into the dough, just so the candy stays put while baking.

Bake bars in the preheated oven for 18 to 20 minutes, or until bars are set and lightly browned. Let cool completely before cutting into bars and serving.