Two four year old girls in my nursery school class were the best of friends. When one entered the room, the other would run to give her a big, welcoming hug. They managed to sit side-by-side throughout all activities and held hands when they walked around the room.
These girls were bright, creative and mature beyond their years. Every so often, something of interest would happen at home and they would turn this idea into a little two girl play.
These plays delighted me so much I’d stop what I was supposed to be doing and watch (from afar, of course).