My 6 yr old asked for a Batman cake. Luckily, he gave me my creative license on interpretation. Instead of extensive piping, I used white and milk chocolate morsels (like for making cookies) to form the symbol and create a nice textured look. Using the smallest morsels you can find creates the best result. Plus, kids alove extra sugar/candy on a cake!
For kids' parties, its easiest to cut a flat cake so I try to stick with single-level cakes in typical baking pan shapes. I started with a 9 x 13 cake pan and used yellow cake. After cooling and freezing, I iced it with canned frosting colored with yellow food coloring. Make sure you mix the coloring in well so there are no white spots that show up when you ice it. For the symbol, I used the internet to find, print and trim out a large version of the symbol. Print 2-3 copies in case you damage one. I cut out the background (so that when you look at the symbol, you can see the whole thing but there is nothing around the outside.) If you are really 'fancy', you can laminate the symbol before starting, but its not necessary. Make sure the icing is dry so it doesn't stick to the paper. Next,with the paper symbol placed on the center of the cake, place the brown morsels around the outside edge. Once done, peel off the symbol and cut the bat shape out of the paper, leaving the hole where it was. Place it back onto the cake and fill in that space with brown morsels. Once done, fill in the middle space between the border and the bat shape with white morsels. Then, I added accents to the corners with squirt icing in black. I did not want to try to color black icing. The squirtable icing worked fine for the accents and I even added his name after taking the photo. Good luck!