you can always serve one cake for guests and make him his own cake with more natural ingredients... you know he eats carrots, so carrot cake with just a touch of icing might be a great idea. You can decorate it traditionally so it would look like a regular cake.
He will get his own cake to smoosh and devour, and everyone else can enjoy a sweeter version...
here is a great recipe for baby carrot cake...
Baby's First Birthday Cake (Carrot Cake)
(Makes 1 double-layer 9-inch square cake; adapted from "What to Expect")
2 1/2 cups thinly sliced carrots
2 1/2 cups apple juice concentrate (you may use slightly less)
1 1/2 cups raisins (optional)
Vegetable Spray/Shortening
2 cups whole-wheat flour
1/2 cup vegetable oil
2 whole eggs
4 egg whites
1 tablespoon vanilla extract
3/4 cup unsweetened applesauce
1/2 cup wheat germ
2 Tbsp low sodium baking powder
1 Tbsp ground cinnamon
Prep: Preheat oven to 350 F. Line two 9 inch square cake pans with waxed paper and spray the paper with vegetable spray/shortening.
1. Combine the carrots with 1 cup plus 2 tablespoons of the juice concentrate in a medium size saucepan.
2. Bring to a boil, then lower the heat and simmer, covered, until carrots are tender, 15 to 20 mins. Puree in a blender of food processor until smooth.
3. Add the raisins and process until finely chopped. Let mixture cool.
4. Combine the flour, wheat germ, baking powder, and cinnamon in a large mixing bowl. Add 1 1/4 cups juice concentrate, the oil, eggs, egg whites, and vanilla; beat just until well mixed. Fold in the carrot puree and applesauce. Pour the batter into the prepared cake pans.
5. Bake until a knife inserted in the center comes out clean, 35 to 40 mins. Cool briefly in the pans, then turn out onto wire racks to cool completely. When cool, frost with Cream Cheese Frosting below or sprinkle a wee bit of powdered sugar if desired.