Possibly the easiest way to simply keep the kids entertained and quiet while you drive is to buy them a portable DVD player (don't forget the headphones). If you have more than one child, then each having their own individual player is the ideal solution, and with players starting at under $200 this can still be a fairly economical solution.
Even one player, with a splitter jack to allow two sets of headphones to be connected, can be a cheap solution.
Doubling as a video "Walkman" is just the start; portable DVD players usually support many other formats, including recordable DVDs (DVD-R⁄-RW, DVD+R⁄+RW), plus VCD and SVCD format discs, MP3s and photo discs (Kodak Photo CD and JPEG files).
A portable DVD player will generally come with an AC adapter and possibly a DC adapter for in-car use. Some players will have a detachable battery, which can be charged separately from the player. Look for a model that gives you at least two hours continuous playback ability for uninterrupted viewing of a whole movie when you're unable to plug-in. Some players last up to five hours before recharging. Rapid charging and the option of a second battery are an advantage also.
Generally speaking, a portable DVD player will have built-in skip protection. This is a built-in memory buffer that helps avoid the video and audio "hiccups" that can arise from the vibration and bumps often experienced while using your DVD player in a moving vehicle. After all, it IS supposed to be used when on the move.
Of course, a big advantage of these laptop players over larger in-car systems is that they simply fold up and fit in your bag or other hand luggage so you can use them anywhere.
For more information, see the Australian PC World our Buyers Guide to Portable DVD players.