Preheat your oven to 350°F (175°C).

In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until smooth.

Beat in the vanilla extract and eggs until well combined.

In another bowl, whisk together flour, baking soda, and salt. Gradually add the dry mixture to the wet mixture.

Fold in the Fruity Pebbles cereal and mini marshmallows until evenly distributed.

Drop tablespoon-sized balls of dough onto a baking sheet lined with parchment paper.

Bake for 10-12 minutes or until the edges are golden but the centers are soft.

Allow to cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.