Prepare cake mix as directed on package, adding 1 tablespoon of the lemon extract and vanilla. Spoon 3 tablespoons of batter into 24 paper-lined muffin cups. Bake as directed on package for cupcakes. Cool cupcakes on wire rack.
Meanwhile, for the bunny feet, microwave white chocolate chips in medium microwavable bowl on HIGH 30 seconds. Stir, then return to microwave and heat in 10-second increments until mostly melted. Stir until completely melted and smooth. Spoon into pastry bag or resealable plastic bag. Snip a small corner from bag. Pipe out 24 pairs of bunny feet using the melted white chocolate onto parchment or wax paper-lined cookie sheet. Try to make pairs that are the same size. Use a toothpick to smooth out any bumps or rough edges, and gently tap the cookie sheet on the counter to help the white chocolate settle. Allow white chocolate to harden (2 minutes in the freezer or 15 minutes in the refrigerator).
For the frosting, beat butter and remaining 2 teaspoons lemon extract in large bowl until light and fluffy. Gradually add confectioners' sugar, beating well after each addition and scraping sides and bottom of bowl frequently. Add milk; beat until light and fluffy. If frosting is too thick to spread, gradually beat in additional milk. Remove half of the frosting and place into medium bowl. Add green food color; mix until evenly blended. Spoon into pastry bag fitted with a grass decorating tip. Set aside. Remove half of the remaining frosting into small bowl. Add 1 to 2 drops red food color; mix until light pink. Spoon into another pastry bag or resealable plastic bag. Snip a very small corner from bag. (The remaining white frosting will be used for the bunny tails.)
Using the pink frosting, pipe out 3 toes and the padding on each bunny foot. Once the frosting has set (about an hour) gently press down on the pink frosting with your finger to create a smoother, cleaner look.
To assemble the cupcakes, pipe green frosting onto each cupcake in a series of short motions to create individual grass spots. Cover the top of each cupcake completely.
For the bunny butts, place cut sides of the marshmallow halves onto each frosted cupcake, leaving room for the bunny feet. Shape remaining white frosting into dime-sized balls, then roll into small bowl with white sprinkles to cover. Pipe a small drop of remaining pink or white frosting onto the top of each marshmallow. Press a bunny tail on top.
Place both bunny feet against the base of the marshmallow with the toes facing downwards.