Cakes are usually associated with sweetness, especially among children. Kids love sweet things and that is why they always see a birthday or any special event as the time to enjoy. For your birthday cake, you could choose chocolate cake. Children and adult would love that. You could also prepare cake that is not too sweet in case of adult guests who are not too interested in sweet things or who are diabetic. Having this combination ensures that everyone has a nice time at your birthday party.
There are ways you could prepare good cakes which everyone would love. Adults like themes like a diary, a champagne bottle, or things which depict a favorite sports character. Therefore, cakes for adults do not need to be that vibrant. You may just have something simple with the name and good wishes of the person written on it. In the case of cakes for kids, you should consider what kids generally like. In the case of birthday parties for children, you could have designs showing baby blocks, puppies, teddy bears, blue skies, flowers, yellow ducks and the like.