How did you introduce the concept of buying / money to your kids?

I gave both my children a piggy bank and encourage savings. my husband and I will give $1 each to both the children for them to save and told them what they can buy with $1 vs many $1. We went supermarket and told them what I will be buying and why am I buying this brand of sauce vs the other brand. We will share with them why we cant buy too many toys. My eldest is 5 yo and she can understand pretty well. H/w, my 2.5 yo is still at the "why" stage.

I bought my daughter a grocery store play set. It included a cash register, play money, grocery items. We play pretend as though we are in an actual grocery store. I use real fruits and vegetables in our play sessions and we use the play money to buy these vegetables and fruits which we later use to make lunch together.

I bought my Daughter a piggy bank at age 18 months and showed her how to put lose coins in

Give a small allowance and a piggy bank