When I moved to London for university, there were 5-6 year olds on buses and trains, accompanied by an older sibling. And they were the rich children attending the private school I lived close to, normal children that age would live close enough to walk to their local school.
Yes, GP appears to be ill-informed about how kids get to school in large parts of the US. In NYC, students take public transit (and are provided passes, if necessary) from approx 13 years old. The same concept applies in most cities I know of on the East Coast (I can't speak for further west, though it appears Chicago has a similar system).
Obviously if people took the time to look at the crime statistics, the chances of being a victim of a crime is less than half of what it was when I walked a mile to elementary school every day.
For more normal crimes, the lifetime chance of being a crime victim is serious. For stranger-on-stranger violent crime, there is a total lifetime probability of about 5.3%.
You might think "oh that is just 5.3% so no big deal", but the chance of dying in a fire is only 0.09% and we still bother with smoke detectors.
Violent crime is a life-altering event. Given the potential for horrific consequences, it is reasonable to be concerned about the possibility. Transportation choices change that risk.
Conversely, are there large cities in other countries that are similar to the US, where this does not happen? I'm going to suspect the Middle East, due to ubiquitous air-conditioning.