The most dangerous place for a child on a cruise ship: a private balcony. A child could -- with the help of a chair -- go over those railings, which are not as high and are straight above the ocean (whereas most public area railings are "tiered" like a wedding cake -- if you fell, you'd fall to a lower floor, just like Chloe did).
We’ve only cruised with Disney

- four sailings, beginning when my kids were 6. Safety was a concern of ours, too (as I'm sure it is with most people).
I used to have a Tag here that said “I prefer the single bath”. That, basically meant we booked the cheapest, inside rooms with no windows (and the only ones with just one bathroom; higher category staterooms had split baths in two separate rooms - which, personally, I don't particularly like). Part of that, of course, was the cost. (IIR our first cruise in 2003 cost just $1600 for four of us, not counting flights and extras.) But it also just felt safe; same with the porthole rooms (having a large, round window that doesn't open).
We did splurge one time for a verandah (private balcony) and here was our experience. The door to the balcony was quite heavy and would've been rather difficult for a child to operate. (I want to say the handle was "child proofed", too, but I can't recall that in detail, exactly.) Our kids were seven on that cruise, and we set rules long before the sailing about when and how they were allowed out there. (A pp mentioned being an EMT - I can relate as I worked in a major pediatric ER for several years, so I was often extra careful with my own kids having experienced some of the crazy, awful, unimaginable things that can happen to kids.) When we did sit out there with them, they weren't allowed to climb on the railings or kneel (not stand) by themselves on a chair up against the railings without us right there with them. Idk how other people handle it.
On a later sailing our kids were older and friends had a verandah and I wasn't too worried at that point as they knew the drill by then and gave us no reason to worry, but we did still supervise.
The one scary thing we did have happen was when we sailed with a large group of friends and family. Our kids were ten then. Around 2am we heard a knock on our stateroom door. It was puzzling as to who it could be, as that had never happened before, but I figured maybe one of our friends was sick and needed help or something. DH went to open the door, and to our shock and amazement, our DS was standing there, outside our room. DH pulled him in. He was apparently sleepwalking, and was mumbling about "going up to watch the sunrise". Yikes!! We hadn't heard him leave the room, but thereafter we put suitcases in front of the door so at least we'd hear him if it ever happened again - which it never has in all our trips on either land or sea. Today we joke with him that we're glad he didn't do a "Peter Pan" off the top deck or something, but it just goes to show that even with the tightest supervision, weird things can sometimes happen.
In this case in the OP, however, I do feel that the RC ship appears to be safe for children. This horrible tragedy would not have happened had it not been for the grandfather's foolish actions. At the beginning of this thread I said I had no sympathy for the grandfather, only for the family, and someone I'm pretty sure said, "Wow". From the beginning of this story I couldn't understand why initial reports weren't believed. It seemed like a lot of people were trying to rationalize his behavior to say that it couldn't be his fault. I still don't understand his reasons for doing what he did, on what should've been such a terrific day. He seemed so cavalier with her safety that it just boggles the mind to think that he could do such a thing with someone he supposedly loved so much. I'm glad to have seen the video because it verifies that those initial reports were probably pretty accurate, and I can see why the PR authorities moved forward with charges. My sympathies still primarily lie with the family. The video proves his actions were not reasonably safe by any means, and personally, I'm glad we can put it to rest, as, really, a whole industry's reputation was at stake.