Can you see how much the pups have grown? Part of this growing is that the pups are now ready for whelping box preparation for later house-training.
The whelping box is now separated into a 1/3 section of newspaper layers & a 2/3 section of fabric for sleeping, nursing, playing with each other & toys (note the plastic bottle behind them--at this stage, a bottle can be great fun and they cannot injure themselves by biting into plastic because their teeth are still tiny and only just breaking through their gums. Of course, the pups also have great, squeaky fabric toys that are not in this shot).
By providing the pups with a place to eliminate that is separate from their sleeping area, pups will generally move to the paper to go rather than go on the blankets. Given a choice, pups are very smart about eliminating away from their sleeping area because it is canine instinct to not dirty where they live. Also, as an important part of her maternal duties, Kit has done a wonderful job keeping the pups and their "nest" clean, which shows pups that their instinctual preference for cleanliness is correct because their mother makes sure this happens.
Of course, the eliminating only on the paper is not 100% ... but, as seems appropriate to say, it's baby steps ...