A common use for the felt squares might be to place just inside the baby's head, after opening the nose up, giving the look of depth to the nostril.
But did you know another use, is to place a square on the inside of the reborn doll kit head, just large enough to cover and line the inside of the face.
On a translucent doll kit, the dark blue of the felt can be seen through the vinyl, from the outside, highlighting the thinner parts of the vinyl on the face, like the temples, eye sockets etc, again giving that additional depth and realism to the skins undertones and base colour. Try it and see for yourself!