Once Upon a Mattress Movie Review
Here's the gist. The prince (Denis O'Hare) can't marry until one of his girlfriends passes the "tests" given by the queen (Carol Burnett), who clearly doesn't want him to be wed -- to anyone. This poses a problem for the princesses in the family, who all want to marry their boyfriends but, by law, aren't allowed to until the prince has a bride. Particularly it's a dilemma for Lady Larken (Zooey Deschanel, in a weird blonde wig), who's pregnant out of wedlock.
Never mind trying to explain that to the kids, you'll have just as much luck trying to get across why our young prince would possibly fall for Winnifred (Tracey Ullman), a strange woman who shows up at the castle one day, seemingly at random. (Oddly, Burnett originated the Ullman role in the original stage production.)
The film is over in a breezy 75 minutes or so, so there's really no time to worry about the story or the singing, or whether this is appropriate for a white-case DVD release. It's ultimately pretty harmless and almost wholly unmemorable, but considerably better than a lot of animated junk that's passed off as kiddie fare.