Thanks to everyone who has responded. These insights are so helpful.
We do a lot of learning/exploring outside of school, too, via CTY, Beast Academy, Khan Academy, learning about politics, geography, etc. My kids also go to a weekly language class (their heritage language) on the weekend and that is the most challenging academic experience they have, which is so good for them (also good socially). We travel a lot, we read a lot, etc etc. They play instruments. They do sports. So I wholeheartedly agree with those who have said that this outside stuff is important. I don't expect the school to do everything.
But - my DH and I both work full time and my kids are still young and while they love to learn, they also want to play and sometimes they need free time to just chill out after school, you know? So the balance can feel off sometimes. And as much as we model learning/exploring at home, I feel their school experience is teaching them the opposite - that school is not really a place for true learning. I hate to see that attitude developing.
I like the idea some of you raised about suggesting a book/online curriculum they could use for those times they are otherwise just sitting alone working on worksheets. Perhaps I can try that.
