Making themed cakes is fun but takes time and patience. It's all worthwhile though, when you see the look on your little one's face when she gets her first glimpse. Most of this Thomas the Train cake is done with icing and food coloring. You don't have to stop with Thomas either. You can make all his friends along with him and have a long cake. This will work well if you are having a large train birthday party with a lot of children.
Bake four cakes. Bake four cakes according to the directions on the cake box. Allow the cakes to cool completely.
Prepare cake your train cake. Cut each cake in half. Place one block on the bottom and frost the top of the cake to act as glue. Place another block of the cake on top of the bottom layer. Repeat the frosting and cake until you have built three to four layers.
Cut the cake so that it resembles the shape of a train--rounded nose at the front and long tail at the back. Insert small wooden dowels to stand vertically in the cake.
Mix food coloring into pre-made fondant icing. Create red, yellow, blue and black. Use the black fondant frosting to cover the front of the cake. Use the blue fondant icing to cover the body of the train. Add red fondant icing to the top and bottom of the train.
Create train sides and wheels. Using a Thomas the Train picture as the guide for your train cake, roll out fondant icing in the appropriate colors to create the sides and wheels of the train. Cut the icing into appropriate shapes and allow 24 hours for the shapes to dry.
Adhere decor to cake. Use water as glue to add the shapes and designs you've created to the train.
Create trim for train. Use the red and yellow fondant to create the trim for the train. Adhere to the train with water.
Create Thomas's face. Use black food coloring to make gray fondant icing for Thomas's face. Use your hands to mold the gray fondant into the shape of Thomas's face. Use black fondant to make his eyes and his mouth with black and white fondant. You can use toothpicks to apply and hold the face on the front of the cake.
If you run out of time, make a trip to a craft store to see if you can get a train cake tin. Then you only have to bake and decorate the themed birthday cake.