While it doesn't look "factory", I have fitted a couple of portable DVD players to our Grand Carnival for the kids.
Works well, they were cheap and can be removed easily if the seats have to be folded down, I am worried about security, or if the kiddies have been playing up
We are investigating fitting an in dash dvd player (Alpine double DIN unit). A adaptor is available to blend the DVD player into the dash. The reason we are looking at this is that a reversing camera can be hooked up to the screen. Some of the Alpine DVD players have the ability to be playing a DVD to remotely mounted screens while also playing music from an ipod or the radio at the same time.