If you've got one large space but you're trying to either, 1) separate the children's area from the adult area, or 2) create small play areas like this "little library," a small area rug can make all the difference.
We have a large living area which is divided into a sitting area and various play areas for our daughter including this little library, a little kitchen, and her little art studio. In order to make the room feel less haphazard, we added different flooring for her play areas. This rug, found on sale at Anthropologie a few years ago, works well in the reading area. For the art studio, we are thinking of a faux distressed wood mat. Be creative, and the flooring you choose will not only define the area, but also make it more life-life.
(Image: Julia Cho)