One of my nieces' and nephew's favorite birthday cakes wasn't one that I decorated elaborately, but that I baked and put borders on, then let them decorate with candy pieces. Sydney has always had a love affair with butterflies so for her 10th birthday I baked a simple butterfly-shaped cake (Wilton pan), piped purple borders and simple wing marking patterns, bought skittles, M & M's, gumballs, and sweet/sour candies and assigned each of them one quarter of the cake space.
Look at those serious faces! They enjoyed it, as you can see in later pics, but they took the decorating seriously, carefully choosing their colors and gently placing the candies on the cake.
Look at those adorable faces!
I'm pretty sure Sydney LOVED her cake, aren't you?