Re: Safety for kids
I would have to ask our instructors for a more complete list (I'm just a longtime student myself), but I know we skip nikyō for the children's classes, along with pretty much anything we wouldn't teach to an adult newbie, like rokkyō (a.k.a. "hijikime", "hijishime"; various other names) or the choking variants of certain other techniques (that is, techniques that end with chokes).
As far as breakfalls go, something like koshinage should be fine for kids: a child training with another child has less height to fall from and less weight to impact the ground with than an adult does. Some preparatory breakfall exercises would still be warranted though. However, I would exclude forced-breakfall versions of shihōnage or kotegaeshi, as those can seriously torque wrists and elbows if the uke isn't fully ready to do so.
Also, take judo as an example: nearly all falls are breakfalls, rather than rolls, and children's programs in judo are commonplace. Yes, you can bring up a counterexample of the child that died in Taiwan, but that was a result of an uncertified, unaffliated, negligent instructor, who was repeatedly throwing the kid himself as some malicious form of "toughening up".