"Think of the children" or not, it really doesn't matter the size of the vehicle. A SmartCar, or even a motorcycle, at 30 mph is likely to kill your kid too.
Assuming weight doesn't matter, it's also a question of visibility. Large SUVs and trucks have such high waistlines and poor front and side visibility that I could easily see a child running out thinking they were visible when they weren't.
Or do you not allow your kids outside either, because you bought a big house with a small yard because that is optimally safe?