I believe that this scenario is very over-blown. If you're in a situation where you have to choose between swerving into another car or hitting a child that darts out onto the street then the question really is: why were you in that situation in the first place? At 20mph pedestrian collisions are almost invariably non-fatal and emergency stops are almost instantaneous. So if you're on a street where a child can appear instantly, why are you going faster than 20mph in the first place?
a child can appear instantly on any street. they can even run into the highway if their parent pulls onto the shoulder for a bathroom break or something.
of course, it's much more likely to happen in a neighborhood than on the highway, so we drive slower in the neighborhood. but anything that can happen eventually will, so there ought to be some policy.
that said, I think there is a certain segment of the population that gets overly excited about mapping the trolley problem onto autonomous driving. I expect that little will change other than the liable party (the car driver vs the company) and it will mostly work out.
sure, but I don't think the whole highway is obligated to slow down for a stopped car on the right shouler, only the lane next to the shoulder (and I would argue that this lane suddenly slowing all the way down to 20mph would create a worse hazard). theoretically the child could make it all the way to to left before being struck. I'm not saying this is likely, just that there is no speed where you can guarantee that you won't hit a pedestrian that is behaving erratically. the best you can do is make it very unlikely in most cases.
