Sorry this is late--I just now saw your question. I have done booties like this many times and have had alot of success with them. You need 6 regular sized marshmallows. I stack two together and hold them by inserting a toothpick into them. I usually let the toothpick extend out of the bottom of the stack so that it is inserted into the cake to hold it in place. A single marshmallow is set in front of and touching the stack to become the toe of the first bootie. Then repeat this procedure for the second bootie and place it next to the first on the cake. I then use a small star tip (#16 or so) to cover the marshmallows. It gives a sort of crocheted effect. I always use a thin ribbon to tie a couple of bows and arrange them on the front like laces.
They are very cute and easy!
A person's a person, no matter how small. -Dr. Seuss
I have done them with Mounds Coconut candy bars and Marshmallows. One section of the Mounds bar for the foot of each bootie, two Marshmallows stacked towards the end for the top of the bootie. # 26 shell tip for piped shells to cover, starting at the base of the Mounds, working around till it is covered, then moving up to the top of the bootie. # 2 string tie bows. A piped buttercream rose inside the top of each bootie.