Especially for Projects for Kids and For Quilts.
I use 100% cotton fabric for almost all my sewing. I just really like it. Occasionally I'll use a blend or another kind of fabric if it's something sentimental for personal use. Some fabric requires special care, or dry cleaning. I'm not talking about those fabrics in this post - I just don't know enough about them. But cotton fabrics, quilting fabrics, cute novelty prints, etc all should be washed first, and here's why:
There's lots of tips out there for quilters about the importance of pre-washing fabrics. Different fabrics may shrink at different rates, even if they're all 100% cotton. If you want your quilt that you've spent hours and weeks and months making to hold up over time, you don't want different parts to shrink and other parts not to, thus pulling or distorting the quit, even tearing it in extreme cases.
While this is an excellent reason to pre-wash all your fabrics, it isn't the most important reason, in my opinion.
When fabrics are made, all kinds of chemicals are used during production, and dying. The chemicals treat the fabrics, and help the colors stay true, and generally assist in production at many stages. However, those chemicals are still there when the finished bolt goes out to stores. The most famous of these is formaldehyde, but other chemicals are used too.
There is no way I want to snuggle under a quilt full of formaldehyde and other chemicals. And there is sure as heck no way I'm letting my child snuggle under that quilt or play with a toy that hasn't had the chemicals washed out of it.
While it may sound too easy that all you have to do to get rid of these horrible chemicals is throw the fabric in the wash, that's really all the experts say you need to do. In all my research, every authority and expert I've found says that as bad as these substances are, washing gets rid of them. It's that simple.
So while it may be a bit time consuming, and, yes, it may require a little bit of pressing if the fabric wrinkles, it's just too important a step to skip. If you are making something that a baby may possibly put in their mouth, (like everything I make) please, PLEASE, PLEASE pre-wash your fabrics.