Drawing. But not drawings of objects. Drawings of marks. Talk with them about the many kinds of interesting marks they can make with different motions of the hand, and with different instruments. Let them start simple and enjoy that, and then slowly combine and
complexify. Have them do some drawing on one piece of paper in two’s and three’s without speaking. Have them do one big drawing on the floor all together unless you feel that would be too chaotic. Keep the steps small. I do this with adults. They’re the same as your kids. You can go on for hours.
Have a wonderful day with them.