I love to paint bird nests.
My client had two pillows and asked me to paint a bird nest on each one.
That was such beautiful fabric and very easy to paint. I used craft paints and fabric medium from Michael's. After they're dry, craft paints are so durable and even wipeable in case they get dirty from handprints, etc.
If you paint on fabric, you have to be very, very careful not to spatter because, in many cases, it's almost impossible to get the paint off without smudges. I always use something to cover up the parts I'm not painting, just to be sure. In case you do spatter, you can use regular rubbing alcohol and a Q-tip to try to remove it. (Be sure to test it first to make sure it won't take your fabric color out.)
The bird nests and ivy were freehand and easy to paint because there was really no structure. But, you could use a stencil or any pattern and that would work well, too.
(I know my nest is a bit "over exposed" from the camera flash, but I'm sure you get the picture!)