Put two-thirds of the buttercream in a bowl and beat in the yellow food colouring. Spread the buttercream in a flat layer over the tops of the cooled cakes using a small palette knife.
Colour the remaining buttercream with the blue food colouring. Put in a piping bag fitted with a writing nozzle, or use a paper piping bag with the merest tip snipped off (see
Pipe simple duck, bunny and chick shapes on to the buttercream-topped cakes. Cut the glacé cherries into thin slices and then into tiny triangles. Use to represent beaks on the ducks and chicks, and tiny eyes on the bunnies.