I was looking into this a while ago with my Nieces and Nephews. If you have one already it's a little less expensive, a simple cradle for an iPad on the head rest does the trick very nicely. Plenty of mounts available and the unit lends itself to whatever they may want to watch, play, etc.
You don't have to worry about connectivity or extra cables besides charging. Not most price conscious option but can also pick up used ones heavily discounted that are just as good and you won't mind when people are rough on them.