Dr Anil has given me permission to help you. I believe what you are discussing is called 'naughty by nature or nurture" and it's been the subject of much debate in scientific and behavioral circles.
Some people believe that when a child is born, they are a blank slate and that whatever is in their surroundings is what will shape their future lives (nurture). While others believe that people who grow up to commit horrible crimes were born that way (nature). 'Born bad' if you will.
The fact is that a large percentage of every criminal that has committed heinous crimes, can be traced back to some type of damage in their childhoods. Either physical or emotional abuse to such a degree that it forever impacted their future behaviors.
Nurture can include psychology, religion, culture, family, friends, teachers, etc. We already know that babies are not born with knowledge (although some seem like they do possess some type of wisdom), but if a baby were left in the wild, it could not fend for itself. Even if a child has less than watchful parents, they don't know not to touch a hot stove, not to jump in the deep end of the pool, not to walk off the stairs, not to be wary of dogs, to walk out into the street and millions of other things.
To answer your question directly, no, I don't believe children are born knowing right from wrong, because a child will seek to fulfill its basic instincts, food, shelter, etc. A child can be molded in their early stages to become just about anything. Lost children from wars have shown time and again, that they are willing to do whatever it takes to survive. Ethics, morals are man made ideologies that are passed onto our children. You have some societies that believe in having more than one wife, while others consider this a crime. Other societies that believe in killing a woman for certain indiscretions, while other societies are horrified by this. Still other societies believe that its ok to take a wife at 12 yrs old, while others don't. There's a million more differences in morals and ethics, that only go to show that a child will believe what he's brought up to believe.
I have seen very young children react in certain situations where it seemed like they would have been too young to understand what they seem to understand, like sharing a toy or food, or comforting another crying child. Some might say if they are old enough to do that then they are old enough to have seen it done, others might say that sympathy and empathy are natural traits that some have or don't have.
To sum things up, you're right...there's no blood test or proof of any of this, because no one in their right mind is willing to isolate a child to gather proof. We do have children that through accident or on purpose have been isolated or abandoned at young ages and all testing points towards antisocial, depressed and many times criminal behavior as the outcome.
I hope this helps, and of course if you want to talk more or need the additional thoughts of a third party for your argument, let me know.