Probably pre-washing would be key, with unidentified fabrics. But especially with drapery fabrics, making quilts for kids, it's probably a good idea to prewash anyway, since some of the finishes on the fabric (either to give sheen or to make them stain resistant) might not be good for kids. (I say that without much real knowledge of what these fabrics are finished with. I just know I got a box of similar remnants and samples once, and I wouldn't have made anything out of them for my kids without washing first.)