I used to be really anal about order and not mixing things or playing with pieces of one set of pieces while playing with another....but after my own kids were grown and gone, I saw the "damage" that can be done by restricting complete freedom with this kind of stuff....
.......so now art (and free play) are times where I simply look the other way and let the kids mix, share, mingle or combine any color (or pieces) they wish to.
It IS a learning experience for them and my need for order should never supercede their need to learn.
