You will need 10 items that snap together if possible. At school, we use unifix cubes. At home, you could use legos of different colors.
If you do not have anything that snaps together, just gather 10 small items such as pennies. You would then need to alter the activity by placing the items in a line on a flat surface and removing items from that line.
1. Count the ten cubes with your child. If this is too many, start with 5 items instead.
2. Explain that you will be taking away some of the cubes and placing them behind your back. Your child will get to see the remaining cubes.
3. Your child's job is to figure out how many cubes you removed and placed behind your back.
4. Your child will need to view the items that are remaining to deduct the answer.
*REMEMBER: It is always important to have children explain their thinking. Ask, how did you figure out how many cubes I have behind my back? How do you know that is the answer? ETC.