How much do you really need to engage your kids?

This is an oddly-worded question: of course I know you need to be responsive to your kids. But I look around at the parents I know and see that, at least ~4 years old, they seem to be constantly working to engage kids, responsive to their every seeming need. And as someone who's going to start trying soon, and is an introvert, this seems completely exhausting. Is this just an American helicopter parent thing or is there a basis for it?

Can anyone direct me toward the actual science of how often kids need to be engaged and how often you can let them do their own thing? I'm particularly interested in research/studies but any input is welcome. I'm just trying to get a sense of what I'm getting myself into.