Sony Playstation 3 parental control failure

I've already dealt with Sony's stance on updating a PSN sub-account to a master account; but it gets worse.

The responsible adult sets up a PS3 user and associates a PSN account with it; they then create another PS3 user for their child and associate a PSN sub-account with it. They set the parental controls and walk away secure in the knowledge that they can't access the internet or 'adult' games or movies.

That is until the child creates a brand new user on the PS3 and associates that with a different PSN account with a fake birthday in which case they've by-passed the lot.

In there any way to stop this? According to Sony, whom I spoke to directly, no.

So what's the point of the parental controls?