I am an American living in the UK and they completely gloss over any US history. While I have a history degree, my children are missing a big part of their history. My wife doesn't really like it when I go on and on about history with my kids, so I am hoping for something that I can play for them in the car or the like.
The History of the United States by The Great Courses is pretty long, well written, and relatively in-depth, although it might be a bit much, depending on your children's age. It's meant for college level students.
It's not a podcast, per se, but you can get it through audible.com if your a member, and if you're not, you can use a free trial to get it for free.