The video I linked to it doesn’t show it, but Peloton’s treadmills do have handrails. Interestingly, there are “under-desk” treadmills available (so you can walk while working at a stand-up desk) that definitely don’t have any handrails.
In addition to start and stop buttons for normal operation, every powered treadmill I’ve seen so far also features a tether you clip to your waistband so that if you fall or otherwise move away from the console while using the machine, it yanks a key (magnetic or mechanical) from the console, causing the machine to quickly shut down (see step 3 here).
That key also provides a way to completely disable the machine while it’s not being used by an adult.
Peloton is technically right in that none of these injuries would have happened if owners had followed the instructions (i.e. remove key when machine is not in use), but of course when you’re manufacturing a machine with the potential to be dangerous, you’re supposed to expect that some users will not follow your instructions, and you’re supposed to take steps to mitigate the harm that might result - e.g. by putting a crossbar under the rear roller to prevent kids and pets from getting drawn underneath the machine by an unstoppable tread. It looks like that last bit is where Peloton came up short.