For long car rides with kids, nothing, but nothing, beats a portable DVD player. (OK, an iPad comes close, assuming you're willing and able to rip all your DVDs ahead of time--and pay $500+ for an iPad.)
If your minivan didn't come with a built-in player, try this: today only, 1 Sale A Day has the Haier PDVD9KIT portable DVD player for $59.99, plus $4.99 for shipping.
The player features a 9-inch wide screen that can swivel--which may not seem like a big deal, but believe me when I say it comes in handy--plus stereo speakers and dual headphone jacks (also very handy).
Haier supplies two sets of earphones, along with a remote, carrying case,
car adapter, and a rechargeable battery. (The rated runtime isn't listed anywhere, but in my experience you can usually get through one movie before needing to recharge.)
I haven't found many reviews of the PDVD9KIT, but its Google Products page has five user reviews that average out to around 4.5 stars. The one complaint I've noticed is the low volume of the built-in speakers. But with headphones, earphones, or external speakers (like the ones in your car), the volume is apparently fine.
Players like this (including this exact model) routinely sell for $100 and up. At $65 out the door, this is definitely worth a look.
Bonus deal: I think by now everyone who wants an e-book reader already has one, but just in case: today only, DailySteals has the refurbished Barnes & Noble Nook 3G + Wi-Fi for $79.99, plus $4.99 for shipping. That's a killer price on the 3G version, though it comes with only a 90-day warranty, not one year like when you buy a refurb from B&N.