I don't think I made myself clear. ... I would say most bad behaviour is from other causes other than learnt behaviour.

JJ, you're making yourself perfectly clear, and from a educational/child development perspective, I'm disagreeing with you.  If a child is born without sin as part of their make-up, they will not sin as part of their behaviour in a perfect world.  Therefore, somehow, they must be learning to do something that is wrong.  Let me take an imprecise comparison.  No baby is born with a specific language in their 'head'.  They will have the innate ability to use language, but they will have to learn a specific one before being able to use it (no-one has the natural ability to speak English, or Japanese, or Swahili, for instance).

What would be interesting to know is just what is going wrong with their upbringing.  Yes, there will be those parents (or siblings) who teach their children to steal or lie (do you know of anyone who was born a pickpocket, for instance?).  Generally, though, parents try to bring up children in a positive way.  If not parents and family members, is it society to blame?  Is it extremes of wealth and poverty?  If so, why aren't all children from extremely wealthy/poor families equally badly behaved?  What is it that modifies the influence of the same parent/social context of two siblings, such that one becomes a doctor, for instance, and the other a burglar.