You will get answers all over the map whenever you ask about pre-washing. I pre-wash everything, unless it's already cut into the size that it needs to be for piecing (e.g. jelly rolls). If the kit is in large pieces, I would pre-wash it. It's not only because of bleeding, but also to get the manufacturing chemicals off the fabric. I just prefer working with fabric that I know has already shrunk and is as clean as possible.