I am making a cake covered in buttercream frosting. I want to roll out some marshmallow fondant and cut out some shapes, like hearts and circles. How do I get them to stick to my buttercream frosting cake?? How far inadvance can I make these shapes, will they be edible?? OR too hard too eat? Will they shrink in size?? can this be done?? I want them to be edible. HELP someone please -my nieces b-day is coming up. Thanks anyone for helping!

To attach just take a frosting bag and put a little bit of frosting on the item to put on cake. Should stick easily. You can make them in advance but they will harden some. If you want them soft then do them as you are finishing the cake. They will not shrink. If you want to make them ahead of time you can put them in a airtight container and they should stay soft too. Then you just have to put a dab of frosting on the back and stick them on.