We took a portable DVD player to Florida (for the plane) and have used it in our car too. In the car my husband used wood for a platform between the two front seats and used velcro to hold the player in place. Worked like a charm. My children, DS 11 and DD 8 used headphones. There is space for two to plug in. It was quite funny to hear laughing out of the blue every now and then. I know you have three children, but my husband said there is something to put on the piece you plug in to make it accomodate another headphone - in other words - two from one.
Without headphones the player did not seem loud enough in the car. Could be I have a noisy car, I don't know.
Anyway, last summer the children enjoyed a movie on the plane to Florida and a movie when we took a trip to Pennsylvania.
We certainly enjoyed having them occupied.
Elke