You asked what I mean about a movie to introduce any subject. I can give you some suggestions on things to look for. Many of these may be available through a local library system.
Charlie Brown (Peanuts) has an American History set that introduces many of those subjects.
School House Rock can be a great resource for History, Government, Multiplication, Science . . . etc.
There are many "documentary" types, even for kids made by National Geographic, The Discovery Channel, The Learning Channel, PBS, etc.
The Magic Schoolbus introduces many science subjects.
1776 and
Ben and Me are good introductions to the Continental Congress and the Declaration of Independence.
I could give you better direction if I knew the particular subjects, but that's a good start