Frost the two smaller cakes with white frosting. A plastic toy palm tree tops the cake. If you're feeling really creative, bake up some gingerbread or sugar-cookie people and decorate them in Hawaiian garb before placing them around the palm tree. Make enough people for each person at the party. Tailor the luau activities to a variety of age groups.
Smaller children can play musical chairs with Hawaiian music for the tunes.
Host a treasure hunt in the outdoor sandbox. Older kids would enjoy having the party in the evening with a real campfire and tiki torches. Whether you hold your party indoors or out, the decorations make it a luau.