The coin used to be put 'naked' into the loaf. Nowadays it is 'sanitised' and wrapped in a piece of silver paper first.
Little hands poke hopeful fingers through their piece trying to find the lucky coin. A clever patriarch will poke about too...before cutting the bread. As he cuts the bread he is always on the lookout for a flash of silver (or bronze) and a very clever father with two children will cut the portions so the coin is in the middle of his two little darlings' pieces....
and there will be no cries of 'but he got it LAST year, it's not fair'.
Usually the coin will be just a 20c piece. I may put a two euro coin in ours this year. Then the receiver will be truly blessed. 2 euros is not to be sneezed at these days.