This activity was taken from https://www.youcubed.org/tasks/snap-it/. (It was actually Day 2 at home. Day 1 was 03/19 and it was Nia’s birthday so we made a cake instead of doing math activities.)
Supplies: Interlocking cubes (unifix or mathlink or others).
What to do: each person makes a chain of 10 cubes. Someone shouts "snap it!" and each person snaps their chain, hiding one part behind their back. The other people have to figure out how many cubes are behind a person's back based on the number of cubes he/she is showing.
The task is explained better in the link above. I also think that the goal is trying to figure out the TOTAL number of cubes behind everyone’s back and not just each individual participant.
Supplies: beads, or anything else small you have at least 20 in your house.
What to do: start with 10 and hide some under a cup when the other people have their back turned or are not looking. My 7 year old said she did it in school and liked the activity.
For more advanced kids:
You can start with a larger number and use the hiding modification. If you do start with 100, it would be helpful to have the 100 beads, cubes, etc. in groups of tens so the kids can get used to seeing how many beads, cubes, etc. quickly by counting by tens first then the leftover units.