What's the etiquette?

What's the etiquette here...

One of the boy's work colleague's 12 year old son wants to be my friend on Facebook.

I have ignore it twice but he still tries to add me, his mum is a friend on FB but I really don't want a 12 year old on my Facebook.

Do I just message the mother and tell her?

Or do I just ignore it?

It just seems creepy cause I am three times his age!