Spray a 9 by 13-inch baking pan with nonstick cooking spray.
In a large saucepan over medium heat, melt the butter. Add the marshmallows and peanut butter and stir until the mixture is melted and creamy. Remove from heat and stir in the vanilla.
Place the rice cereal in a large bowl. Pour the melted butter mixture over the cereal and stir until well coated. Stir in the Oreos. Press into the prepared pan in an even layer. Let cool and harden.
To make the chocolate peanut butter topping:
In a microwave-safe bowl combine the chocolate chips and peanut butter. Microwave for 1 minute on high speed. Stir and continue microwaving in 30-second bursts until melted and smooth.
Let cool for 5 minutes before pouring in an even layer over the cereal layer. Sprinkle evenly with rainbow sprinkles Cover with plastic wrap and refrigerate or freeze until very firm before cutting into bars.