The original idea comes from the wonderful website Family Fun. The link contains a detailed explanation of the cake's decoration, but the idea is fairly simple:
I covered the cake with whipped cream, and put gummy sour worms and Gummy Bears in their proper places as seen in the photos (of course, any other sweet or snack with a similar shape will do). I made the starting circle using two more Gummy Bears: I carefully cut their ears, legs and arms, which come rather close to a round shape. Cylindrical wafers, such as Pirouette cookies, form the rod handles. Each is secured to the cake with a toothpick (it is best to add these in the last minute; otherwise they lose their crispness).
My two additions to this cake are the chocolate goal posts (instead of using licorice) and the spectators' benches.
Preparing the chocolate goal posts requires some dish with an appropriate shape, reminiscent of goal posts. This may require some imagination; here are the goal posts I made while still in the bowl, to illustrate a possible shape - a square with rounded corners:
Melt some bittersweet chocolate (in a microwave or double boiler. When melting in a microwave, break the chocolate to small pieces and heat for no more than 10-20 seconds at a time, mixing well after each heating, to avoid burning). Cover the bowl with baking paper and tighten well (it's a good idea to use an adhesive tape). Use a spoon's or a teaspoon's handle, a brush or any other tool to "paint" with the melted chocolate on the paper. Use toothpicks to draw the fine lines. Freeze for about an hour and then repeat the process, drawing a second layer and making the chocolate twice as thick and strong. After the second freezing, gently remove the paper from the bowl, and then - very carefully - remove the paper from the chocolate. This is best done as soon as possible to serving the cake, but if done beforehand, it is advisable to fit the paper back in the bowl, and put the chocolate back on the paper (no need for precision), so that the chocolate remains chilled and protected until the cake is served - and only prior to that, put it on the cake.
The spectators are some more Gummy Bears, leaning on some more cylindrical wafers. Spread a line of melted chocolate to "stick" the wafers, and another line in front of it, to help stick the Gummy Bears as shown in the photos.
Finally, the soccer balls (or footballs) are, of-course, the birthday candles.
Bon appetit! :-)