You don't have kids, do you?

Addition and subtraction are abstract concepts that are learned around age 5-6. It starts with tangible objects, pictures, ect.

Cash is a tangible object that helps teach the concept.

I certainly didn’t. I remember getting cash as a young child, thinking with $20 I was “rich”, and rapidly blowing it on Sim City.

I only understood the value of money once I both had a bank account and a job that funded it.