Our kids know I can see anything they ask. As well as any time spent on devices. I don't see this as very different from my upbringing. And I haven't noticed any regression in trust.
It is (was?) easy to control your browser's history. It is impossible to control what these devices send to google/amazon.
Your browser's search history only gets populated when you, well, search. These devices are collecting information 24/7, regardless if you are actively engaged with them.