Children and how they can tell us apart

I do not know how many of you have noticed this but it is so very obvious to me. I am talking about young children and how they recognize instantly whether you are a male or female. I mean the first time a child meets someone, it instinctively knows which sex the other person is and addresses them appropriately. Believe me when I say this is not the way adults recognize, which is ofcourse purily based on visual reception. I guess children have some inbuilt recognition mechanism. Having been around many young children (my dear niece and sweet nephew and others..) I have observed this many times- Especially when I wear unisex clothes like Pants and shirt, they r clearly able to distinguish me as a female and call me 'akka' ! I do not know of any thoeries relating to this in Biology or any other related subject so the credit for discovering this concept first shall go to me. And I will name it Sex recognition concept -like revenue recognition concept in Accounting ;) or may be VJ's theory of sex recognition in young children.