A great multihull for kids in the optimist age and size range is the Windrider 10. We use these boats in some kids programs and we have the kids out sailing a triangle course in less than an hour (they are actually on the water in about 15 minutes). It is not the traditional yacht club way of learning to sail but kids are hooked quickly on the speed and simplicity of the boat. The boats are relatively inexpensive, car toppable and are a great boat to get young kids hooked on sailing and multihulls. You should check one out!