Even if they were so inclined, many parents have a pretty reasonable expectation that their kids wouldn't be able to just hop in their car and take it anywhere. At least, not until they hit their teenage years.
But while it doesn't happen often, it's not unheard of for children as young as five to figure out how to do exactly that. Of course, they often come to realize that they're in way over their heads when they actually try it.
And while I have older relatives who were able to pull this stunt at 13-years-old without getting caught, one child has the distinction of both being not quite that lucky and far luckier than he may realize.