There is also an interesting point, that is, two years olds may know good because they are good. They have been born of goodness, purity,and without sin, they have not sinned and dont know how to.
But as kids get older they unfortunately see the evil around them, and some succomb to it. I think religion is a way to remind people of common sense, because we forget, and fall to pressure from others and need a reminder.
Another point to it is also, two years olds are very selfish, very ignorant, very trusting, very vulnerable, and weak.
We were and are created to depend on something, someone all the time.