In the last few days, I've seen three kids who couldn't have been over 12 playing completely unattended on the rocks at the edge of the *very* storm-swollen Bosque River at around 10:30PM in a closed section of the park, and a kid who might have been 5 riding a scooter down a residential street for at least three blocks just before rush hour. No parents in sight, nor any indication the parents think there's anything wrong with it. There have been a few parents taken to task over the years about turning their <10 year old kids loose in the park and leaving. Their argument is always that it's a park, so it's supposed to be safe. I can't imagine what would constitute a looser rein for these kids.
Let me help then.
When I was 10, my parents would routinely (as in several times a week) but me on a sled behind three trained husky's and turn me loose for a 6 mile run. The trail was a loop, but there were longer ones, and if I took a wrong turn (as I did once or twice) 20-25 miles was available. A couple wrong turns took me into several hundred square miles of military reservation with maybe live/maybe not ranges. By the time I was the 12 years old of your river watchers it was reasonably routine for my mom to drop me and my dogs (5-8 by now) off Sat morning in the 23,000 sqmi Mat-Su Valley with a predetermined pick up spot and time (Sun afternoon 80 or so miles away from the start). This was pre cell phone, pre-PLB, pre-affordable handheld GPS. I had a USGS map and surplus lensatic compass. Now I will admit that my Mom had a pretty dang loose rein, even for then, but perhaps if we taught kids to take care of themselves as early as possible, they'd move out before their age started with a "3".
On the gorilla and kid, don't know enough about mom and kid. Kids can be pretty sneaky at getting what they want and carpeing their diem. Maybe she was negligent, maybe her kid is smart. Maybe both. Doesn't really matter in anything but the finger pointing. Once the kid was in the custody of the ape, and the ape didn't give him right up, there was only one outcome, and the zoo did the right thing. Sometimes the right thing sucks. Kid vs. Gorilla? Seriously, Kid every time. If it was Kanye vs. Gorilla there might be some question but not a 4 YO.