Current F-Secure Mobile Security (or F-Secure SAFE/Total for Android platform) with remote control for Parental Control features (family rules).
So, you did set-up for your Samsung tablet as ability to give it to your child safely. And youtube is blocked as certain category ('social media' as example). With your certain situation -> when you try to use this device -> you want to see youtube (which blocked as expected action if your child try to do so). Right?
If so, I'm not sure about any common workarounds. Currently -> looks like that not possible to "allow" page with kids-profile under Android application. And I able to suspect that this is 'as designed'.
Maybe possible to ask F-Secure Team about feature like "remote control for allow/deny website's lists" (as ability to allow only certain website from restricted category).
If 'social media' (as reason for block youtube) should not be restricted. Required steps are:
--> login to your (main) My F-Secure Account portal.
--> choose kids profile and "Parental Control" settings about Content Blocker categories.
Another options -> tries to break "Parental Control" design by some steps.
Sorry for my long reply. Maybe possible to provide more information "why not possible to see youtube" with your certain situation (how it visible that 'it not work/not possible to see youtube'). If previous suggestions about something else than your situation.
And sorry for my worst English.