Best form of protection for your children is some quality parenting (and vetting of internet access, phone use, and friends)!
When my eldest was just a toddler, he started to tear up a free newspaper at my mothers.
I told him to stop - but she simply said "It doesn't matter, it is free and unwanted"
To which I replied "When he can tell the difference between a free newspaper and a family bible, he can tear it up - until then he will be told NO."
Putting electronics in the car is no substitute for taking the time to teach the things that are important, even if it means going on private land and letting them scare themselves in safety with you in the vehicle.
Anything else, and you are simply postponing the time when they try it for themselves at the wrong time or wrong place.