Teach the kids the US Constitution

At the end of the American Revolution there were 13 independent colonies.  Each colony had its own legislature to make laws, a governor to execute them, courts to enforce them, an army, a navy, a diplomatic corps, taxes, and an establishment that ran things.  In short everything you need to become an independent nation.  And the people who were the colonial establishment, the colonial legislature, the administration and the courts, wanted to keep their jobs, their influence, and their position.  They all feared a Continental government would usurp their powers, position and livelihood. 
   On the other hand they all feared the British would be back for round two. They all knew that none of them were strong enough to stand off the Redcoats single handed.  They knew they needed to present a united front to a hostile world.  They also knew that the existing Articles of Confederation were not working.  The Confederation lacked even the power to levy its own taxes. 
   So, when the call to a Constitutional Convention went out over George Washington's signature, all the colonies sent a delegation.  All the delegations were intent upon setting up a federal government to handle foreign affairs and national defense  but not one that took over their jobs back home.  Hence a lot of careful language in the Constitution outlining just what powers the new federal government might have, and those powers it would not have. 
   Kids ought to understand the separation of powers into the three branches of the Federal government.  Article 1 creates the Congress to make the laws.  Article 2 sets up the Executive branch to execute existing law but without power to make new law.  Article 3 sets up the federal courts and defines their jurisdiction.  Note that the state courts existing at the time handled ordinary criminal and civil matters and the federal courts were restricted to matters of federal law.  They cannot try a defendant for murder, murder is a state crime, not a federal one. 
   The Constitution had a lot of compromises and on the whole was a very successful document.  It still controls the United States today, with a mere 27 amendments over 230 years.   Of those 27, ten were applied right after the adoption of the Constitution and should really be considered part of the original deal.  That leaves a mere 17 amendments over the course of 230 years, a pretty good record for stability.