It seems that the new version of Norton Family for Android has removed the ability to block websites in external browsers (like previously, in browsers such as Chrome for Android). The release notes are lacking for the new version but from my testing it seems to not block sites in any browser other than the Norton Family browser now introduced.
If so, it’s a terrible move as the change was made without notifying customers. I only found out because my son was able to access block sites all of a sudden.