Moste everyone said this already, but thought I would throw in my two cents. Simple squares would be better than triangles. I can't really remember when kids start learning geometry but they may get really confused by the need to cut pieces 3/8" larger. There is also a lot more room for error in a triangle and kids to tend to get frustrated and give up when something doesn't work out very well. Simple squares may seem boring to us, but if the fabric itself has lots of cool colors and interesting patterns, that in itself will make them happy and want to so it together. Hope that helps. It sounds like a lot of fun. I just love teaching young ones (or old ones) new things and watching the light bulb turn on.