What it teaches
Adding with coins, and the fact that the same amount can be made several ways. Four coins or two โ both can be right, and being asked to choose is where the thinking is.
Money is also the first place most children meet the idea that a single object can be worth more than another single object. A five is worth more than three ones, and that is not obvious when you are six.
What to look for
Watch whether the child starts with the biggest coin. Reaching for the largest coin first is the efficient strategy and it is not obvious; children who find it have understood something real about the values.
When paying is comfortable, Working out change is the harder half.