There are many ways to monitor and restrict students online, here are some resources that some parents have found helpful.
Supervising Google Accounts/Family Link: This is an option for students working on their personal chromebook/with their personal google account: https://support.google.com/families/answer/9055704?hl=en
Restrictions through your Wifi Router: The instructions for this will vary depending upon your wifi router (you may need to search for or dig out the manual), but here's an overview of setting up controls: https://www.cnet.com/how-to/how-to-use-your-router-parental-controls-pause-wifi-kids-internet/