Civics for Middle School

Hello!  My son is 11 and will be in 6th grade this fall.  We would like to take this year to learn about American government and civics, especially since it’s an election year.  I’m obviously not looking for anything as in depth as high school, but basics like, What’s a democratic republic (and how is it different than a democracy or republic?), what are the roles and responsibilities of citizens, the branches of government.  I’m not finding a curriculum or even good books that aren’t too in depth (we still love picture books, too, if there are any that are appropriate!), but I’m sure I’m just missing them.  Thanks for any advice!!