Force restricted YouTube settings on managed chromebooks

[Norma Brooks]

Hello,

I'm hoping someone has a magic answer for how to do this.... 

We use chromebooks and have always allowed students to log into a personal gmail account on their chromebook after signing into the device initially with their school account. This has helped our votech students still access their CTC accounts in addition to our district accounts. 

We now have a string of occurrences of where students are able to access YouTube unrestricted because they are logging in with a personal account. We do force YouTube restrictions when they are logged into YouTube with their district account, but all they have to do is switch over to their personal and they now have open access. Interestingly, this has not been a problem for us until now and we've had Chromebooks for 8+ years. 

From what we can tell, you can force SafeSearch in the Admin Console on the device, but we are having a hard time finding out if it is possible to force restricted YouTube settings on a managed device (rather than just on an account). Hoping someone has some advice or insight on this! Thanks so much in advance!!