honestly, the parental controls Amazon offers are surprisingly robust but buried in a few different places. You've got to start with the actual Amazon Household setup on the website—it's the foundation. Create a child profile through Amazon Household first, then you link that profile to the specific Kindle device. The dashboard on the Parent Dashboard page lets you set daily reading goals, which is neat, but the real filters are in the 'Content' section. You can block access to the web browser entirely, which I did immediately, and restrict the Kindle Store to only show books from the Kids category. The age filter based on Amazon's ratings is there too, but I find it a bit hit-or-miss; sometimes stuff slips through.
What's less obvious is managing the 'Library' view on the device itself. Even with a child profile, if you've previously downloaded books from your adult account, they might still be visible in the 'All' tab. You have to go into the kid's profile settings on the device and make sure it's set to only show content from their profile. The FreeTime controls, now called Amazon Kids+, are a whole other layer—you can set time limits for reading vs. games, and see a detailed activity report. It's a bit of a puzzle to get everything locked down, but once it's done, it's pretty solid. I still check in on the Parent Dashboard every few weeks just to see what's been read.