fkelly1165 -- Thanks for reaching out. I pulled up your account & it looks like you have an xFi eligible Gateway. You can make use of the Xfinity xFi Mobile App or Website to do this. First you would want to set up a profile for your son in the app and assign his devices to that profile. Once you've done that, you can set up a Bedtime Mode for that profile.
You can read more about Profiles and Bedtime Mode here --