Combine the white cake mix, melted butter, eggs, and vanilla in a mixing bowl. Mix everything until well combined.
Add in the milk and the Easter/Spring sprinkles and stir until combined.
Line a muffin tin with cupcake liners, and scoop in batter into liners until 2/3 full.
Bake for 18-20 minutes, or until the toothpick placed into the center of the cupcakes comes out clean. Set cupcakes aside to cool completely before frosting.
To make the frosting, begin by beating the softened butter in a mixing bowl until it's creamy. Then, slowly add in the powdered sugar, one cup at a time, while continuing to mix until well combined.
Next, add the vanilla extract and mix again.
Finally, add the milk, one tablespoon at a time. (You can adjust the amount of milk to achieve your desired consistency.)
Add green coloring, if desired, and stir until frosting is the color you want.
Once you've achieved the desired consistency and color for your frosting, grab a piping bag and cut off about 1/2 inch from the tip.
Secure a grass decorating tip (such as the Wilton 233 tip) into the piping bag and fill it with frosting.
Begin piping the grass onto your cupcakes, covering the entire surface.
Finish off the decoration by adding bunny ear candies and sprinkles.
Notes
The frosted cupcakes should be stored in an airtight container in the refrigerator for up to 4 days. This keeps the frosting set. You can allow them to come to room temperature before serving.