James Martin/CNET

It's tough being a kid. Problems like peer pressure, sudden unexplained growth spurts, and the heartache of first love leave youngsters with a lot of questions -- but they can't turn to Microsoft Cortana for answers.

Microsoft's new voice-activated virtual assistant for Windows Phone falls foul of US child-protection rules and can't be used by anyone under the age of 13.

If anyone under the age of 13 asks Cortana for help, it responds with, "I'm sorry, you'll need to be bit older before I can help you."

Come and get me, COPPA

Named for the AI computer from the "Halo" games, Cortana is a virtual personal assistant that responds to your spoken questions and commands, looking up information for you or controlling your Windows Phone. It gets to know you, in the process collecting data and sending it to Microsoft's servers. That means Cortana falls under the auspices of the US government's Children's Online Privacy Protection Act, or COPPA.

COPPA polices the information young'uns can share online without the consent of a parental unit. Cortana doesn't have the necessary parental controls -- but then it is only in beta at this stage. I've contacted Microsoft to ask if the situation will change when Cortana goes public.

Cortana and Windows Phone 8.1 are currently available to developers. It's in a Microsoft forum that the issue has emerged, with a developer asking Microsoft to help their young daughter try the technology out.

Of course, Cortana only knows how old you are if you tell it. It's unclear whether fudging your date of birth will cajole Cortana into chatting with you if you're under 13.

Cortana is part of Windows Phone 8.1, and takes on rival virtual assistants such as Android's Google Now and Apple's Siri for the iPhone. As well as answering your questions and commands, Cortana has a sense of humour and even sasses you back, the cheeky scamp.