Grease a 9x9 inch baking dish with cooking spray or butter to prevent sticking.

In a large saucepan, melt the butter over low heat, stirring gently to avoid browning.

Add the mini marshmallows and vanilla extract to the melted butter. Stir continuously until the mixture is smooth and the marshmallows are fully melted.

Remove the pan from heat and gently fold in the colorful cereal until well-coated with the marshmallow mixture.

Pour the mixture into the prepared baking dish and use a spatula to spread it evenly. Press down lightly to create an even surface without compacting too much.

Allow the treats to cool at room temperature for about 30 minutes, then cut into squares or rectangles.

Serve and enjoy your homemade treats!