Activity 1: - understanding that the total remains the same no matter how things are grouped.
Collect resources; stones, sticks, pasta, pencils, cars anything.
You select a number, your child then counts out the correct quantity of objects.
Ask your child to split these into 2 groups initially. Get them to count how many is in each group. Then ask them how many altogether?
If your child goes to count them all, let them. This tells you they do not yet understand that the total remains the same.
Your child may have to do this several / dozens of times. Eventually they will realise that they do not have to count as nothing was added or taken away from the original amount.
Play with splitting the objects into 3, 4, 5 groups. Have the objects spread far apart, then in lines, in heaps etc. For young children, when objects look visually different they believe the total alters until they fully grasp this concept. Then you will no longer be able to trick them!