@umbra21 - Unfortunately, most of those are made of nylon which don't accept fabric paints as well as materials like cotton or silk. You might want to get your kids some handkerchiefs or something to paint instead, if you don't want them to go nuts on their own clothes.
Adults can use fabric paints as well. I've found it really soothing and effective to use a lot of colors on a silk or cotton scarf. Even if you aren't an artist, the picture will most likely be difficult to see when you're wearing the item, but it looks very effective.
I always have people ask me where I got them and it's nice to be able to admit that you made it yourself.