Soldato
In the OPS case if he was going 5MPH faster he would have caused more serious injures and quite rightly could be at fault. If he was driving 5MPH slower then there would be no collision and that is obviously a safe speed.
And if he was going 10mph faster he would have been past the place the child ran out into the path of the car before the child had a chance to, meaning there would have been no collision so that is also a safe speed.
It is completely possible for the OP to have been at a standstill on the road in traffic and the child still run out into the road into the side of the OP's car fast enough to cause injury. Is this still the fault of the driver?