Cut 4 of the milk chocolate buttons in half. Melt the white chocolate in a small dish in the microwave, and use a toothpick to draw a 'paw print' on each piece (see photos for a guide). Place flat on a plate, and leave to set completely.
Meanwhile, melt a few squares of milk chocolate. If needed, trim one end of the mini marshmallows so they're a little shorter, then use a dab of melted chocolate to stick them onto the wide end of each Creme Egg, slightly off to one side.
Cut the remaining four milk chocolate buttons in half, and use some more melted milk chocolate to stick them to the narrower end of the Creme Eggs (the 'ears' - see photos for a guide). You'll need to hold them in place for 30 seconds or so until the chocolate sets enough to hold them - but be careful not to melt the chocolate with the warmth of your hands.
Use some more melted chocolate to stick the bunny 'feet' to the base of each Creme Egg, either side of the marshmallow 'tails'.
Store the Creme Egg bunny bums in the fridge until ready to serve.