Ben's Guide to U.S. Government for kids, named for Massachusetts’ native son, Benjamin Franklin, is a 6 part series on our United States Government at http://bensguide.gpo.gov/. Ben Franklin was a printer, librarian, inventor and statesman. One can learn about his life on the website.
The guide covers grades Kindergarten through 12 and it includes a section for parents and teachers. On this website you can learn about: animals, arts, business, money, careers, computers, crime, justice, education, environment, health, national security and many more topics.
You can also find basic information about the U.S. Government and its agencies which is helpful to parents as well as kids. It is quite possible that among the varied agencies listed are some that may not be known to you before.