How can we teach our pre-schoolers mathematics?

FRESH MEMORY:

Years ago, I took my son with me to grocery store. I knew I only had $20.00 I could spend. As we walked into the store, my son asked me, "Mom, can I get a pack of gum?" The gum pack at the time was only $.25, but I knew I had a long list to purchase. "If there is any money left over and I have enough for your pack of gum, yes!" I told him. He agreed to this.

It was winter, so my son took his jacket and stuffed it on the lower level of the basket. I cautioned him about
keeping his hands away from the wheels. He seemed comfortable enough that I forgot he was there. After at least 20 minutes, I arrived at the cashier. I began putting food items and other necessities on the conveyer belt, getting them ready for the cashier.

My son at that moment said, "Can I have it, Mom?"
"What?," I asked.
"The gum!" he insisted.

Oh yes, "the gum," I thought....I took a quick look at all that was on the belt and figured I was probably Over, not Under.
"Remember what I told you; only if I have enough." I reminded him.
"You do have enough." he retorted.
"Bill, I only have $20.00." I said.
"But everything you bought adds up to only $19.69." he said with total assurance.

The cashier and I looked at each other with a smile - wasn't he cute to say that? Then something amazing happened. The cashier added it all up, including tax on those things that were taxed by the state.

She looked up and said, "How did your son do that?"
I really wasn't paying attention and asked her, "What? Do what?"
"He added up everything, including the tax and got the right answer." she shockingly explained.
"He did?" He asked.
"Yes! and you do have enough for that pack of gun too." She exclaimed with a smile on her face.

Wow! I almost had to stop and think about what had happened. My son is only 4 years old and he is doing difficult Mathematics! How did this happen? No one sat down and showed him. Was he a genius and I never knew it?

No! Since he was two years old, we had been giving him pennies. We gave him a bank and fed him pennies, whenever we had them. We would count to ten with him and he would drop the pennies into the bank. Clink,
clink, clink! By the age of 3, he was running back and forth to his bedroom with pennies. One, Two, Three, four....twenty one, twenty two, twenty-three, twenty-four....thirty-one, thirty-two....forty-one, forty- two...and on to the hundreds and plus there. He just saw it as a game and we loved that he was learning something most kids didn't learn until they attended school. But what we didn't know was that he was also learning other things about numbers....how to add them to each other.

Needless to say, Bill got his pack of gum and eventually, when he was in 6th grade, began buying bubble gum and started his first small business of selling gum to kids at school. He made a killing.