Teaching about free markets is like teaching about spherical cows. But this isn't really on-topic.
Thanks for illustrating my point that people in American classrooms should be taught about it.
More to the point, in my experience the people who say free markets are some crazy extremist unworkable ideology tend to have very strange ideas about what it is. For a typical example, they'll claim a free market requires "perfect information", which is completely false. (Imperfect information is called "risk" and is factored into prices.)
Spherical cows aren't useless though. Unless of course you mistake the map for the territory.
As with everything in economics one side thinks the other is dangerously simplifying whilst they themselves are fully aware of the nuance.
I don't have the time, energy or expertise to marshal the evidence but I don't know anyone with all their marbles that thinks that an utterly unbounded free market with no restraints would be a good thing. I don't think you believe that either.
Teach them about bailouts as well.
What should a teacher answer when someone makes the point that Boeing is the only airliner manufacturer in the country?
One answer is that it is so expensive to develop a new airliner, and so expensive to set up a production line for it (each one is pretty much a "bet the company" thing), and the market for airliners is so limited, that there isn't room for many manufacturers.
As for bailouts, Boeing's competitor Airbus is funded by the European taxpayers.
This topic is more suitable for college level. In grade school, simply dissecting how a lemonade stand works is good for starters.
They should also teach basic accounting. (It really isn't hard, it's not much more than adding and subtracting. People really ought to know the difference between "profit" and "revenue", as they are often conflated.)