This idea comes from our friend Ashley Poskin. Blackout fabric is available at most craft stores to purchase by the yard. Once you've purchased your fabric, it's simply a matter of cutting it down to size (first, measure for hanging a set of curtains), placing an iron-on adhesive strip, and bonding the backing with heat. (We used Stitch Witchery, which is a fusible bonding web that permanently bonds two layers of fabric together with the heat of an iron—plus, it's machine washable.)
When purchasing blackout fabric, you have a few options: a lightweight fabric that feels less like vinyl, but lets in more light (if you're working with a medium- to heavy-weight curtain fabric, this is a good option). Otherwise, if your curtain fabric is very see-through, you'll want to choose a heavier weight blackout fabric, which feels slightly similar to vinyl. If you find yourself at the store and unsure of what to choose, turn on the flashlight function in your phone and hold the light directly behind the blackout fabric to see how much light actually shines through. Your other option is color—white, off-white, ecru, and gray—to be complementary or a pretty contrast to your curtains. Blackout fabric is one of the many ways you can personalize your curtains.
For parents, blackout curtains in a kids room can mean a priceless extra hour of sleep for their little ones. They also come in handy if you're a night owl and aren't quite ready to greet the day as the sun comes up.