The problem with this line of reasoning is that it assumes that the goal-directness comes from the smarter part of the duo decision-maker and bearer of consequences. With children and animals we consider they preferences as an input into our decision making, which mainly seeks to satisfies our preferences. We do not raise children solely for the purpose of satisfying their preferences.
This is why Rohin stresses particuarly on the idea that the danger in is the source of goal-directedness and if it comes from humans, then we are safer.
We raise children to satisfy their expected well being, not their naive preferences (for chocolate and toys), and that seems similar to what a smarter-than-human AI would do to/for us. Which was my point.
I think we raise children to satisfy our common expected wellbeing (our + theirs + the overall societal one). Thus, the goal-directness comes from society as a whole. I think there is a key difference between this system and one where a a smarter-than-human AI focuses solely on the well-being of its users, even if it does Context Etrapolated Volition, which I think is what you are referring to when you talk about expected well being (which I agree that if you look only at their CEV-like property the two systems are equivalent).