Theology divides evil into two types: natural and moral. Natural evil are things that happen when no free will choice is involved. Moral evil is the result of evil free will choices.
Natural events/calamities are not accidents, they still come about through cause and effect.
The driver has been charged , so at this stage it seems he did something in his free will to effect the fate of those children., so no mere accident.
You don't seem to understand what free will is. Free will is a choice by a sentient mind. A random brake failure has a cause and effect, but is still not due to free will.
This specific case does not matter. The general case is that the car may have been maliciously driven by a person or there may have been a random failure which caused the accident.
