Modern thinking is that if hit by a car at 20 mph you will probably survive. If hit by a car at 40 mph you will probably die. Your injuries result from the energy transferred from the vehicle, so at any given speed a lighter vehicle is less likely to kill you than a heavy vehicle. By that single metric a 1960's Ford Cortina is less likely to kill a pedestrian than a modern Ford Puma (or it can be travelling faster before it becomes a danger to life). Working against the Cortina is that mechanically it was not designed with pedestrian safety in mind, but fixing that wouldn't require it to be bigger. However, making the front taller (like on the Puma) means vital organs are more likely to be impacted in a collision. Whilst the Puma is not especially hostile to an adult, that extra height could make all the difference in the case of a child.
