A popular theme that works well for either a boy or a girl is a clown or other circus_related cake. They are usually very bright and colorful, which makes for instant attraction and a great focal point for a party table.
People love chocolate cakes and cakes containing chocolate is one of the most important things for any birthday party. Chocolate also symbolizes a lot of things like joy, love and bond between lovers. Therefore, birthday cakes are making people express love to one another.