In what circumstances would it be best for a child to not know there parents, if any/
I'd say it's different for each kid.
Perhaps they acknowledge their new parents to be the parents that they have always had, others might need closure and would want to seek out their original parents. I'd say it's their choice to make and if they bring it up, it's definitely worth looking into. Other then that, I don't think it's anyone's call but their's.
I think it's better if a child knows who their parents are because when they get older they will be curious and they will go searching for them... It's a big part of where they came from and who they are...
SOmetimes. SOme parents can be real crappy. That's why adoptions exist.