Imo the biggest problem when introducing children to these devices is how to get them to understand that this is very different from an actual human. Even if you find proper wording that a 4yo would understand, these words are easily overwhelmed by the fact that you can talk to it like a normal person. It's already interesting to watch children slowly grasp the concept of (video) calls, but then taking the next step and understanding there isn't a person at the other end of the Alexa dot is yet another step, because if it isn't a human, what else is it?