Resting the camera on the dashboard of the car to keep it relatively stable would be a good approach. Then it's just the car's movement and the cars outside that will create the blur and not camera shake. This will have to be experimental as far as shutter speeds and exposure are concerned. Obviously night time would work best if I am going to record light streaks. The camera pointing at back seat and kids with blur outside?
“When you were a wandering desire in the mist, I too was there, a wandering desire. Then we sought one another, and out of our eagerness dreams were born. And dreams were time limitless, and dreams were space without measure.” ― Kahlil Gibran