Google's Family Link has been working really well for us.
We're using Family Link on our boys' phones and my eldest's ChromeBook. It's with the latter I'm finding some frustration, eg in their wisdom Google have decided that no child account will be allowed to access YouTube, whether it be the website or the app. Sorry, but I'd rather they let me as the parent determine whether I trust my kid to use YouTube or not, rather than it being out of my hands.
I think we're also going to hit a limitation in that the school will provide their own Google account for access via the ChromeBook, thereby rendering the otherwise useful controls (eg limiting access by time of day) useless.