Parents need to know that many of the songs provide lyrical devices to help children memorize facts like the multiplication tables or the Preamble to the Constitution. A narrative approach is used in many tracks to explain historical developments and, in one case, the legislative process ("I'm just a bill and I'm sittin' here on Capitol Hill ...").
Though this is a review for the CD, the DVD is really more versatile (but not included in "movies" on this site.) I use the grammar rock DVD in my high school English classroom. It is really the best tool to teach parts of speech, which most high schoolers are expected to know but which most English teachers never teach! Though the target audience is elementary school (remember you watched the Superfriends and then caught a Schoolhouse Rock cartoon?), the music is excellent for any age. The grammar rock can serve at any age, the history probably useful through junior high, and science and math are likely most useful for elementary school.
I am also the mom of three, and my kids have watched the DVD from the age of 2. I don't care how much they watch it, because what they are memorizing is grammar, math, history. The DVD lets you choose to play all the cartoons in order (grammar rock together, history rock together, etc) or mix everything up. My 6 and 8 year olds enjoy controlling this.
Some are better than others: the grammar rock are all good; some science is outdated; there is one "Dollars and Cents" which has a country theme, and terrible grammar ("ain't" and "got me"); Schoolhouse Rock was infamous for being a good television role model for people of color (Verb's "That's What's Happening" features African American characters, for example)