Two most common issues that a parent can, unintentionally, cause in a child are poor perfomance in education or other areas, and aggression at home or school.
Some parents exert a lot of unhealthy pressure on their children and eventually the children buckle under such pressure. This leads to avoidance behavior, poor memory, lack of concentration, exam fear, study anxiety, and other such issues.
Aggression in a child can be a direct result of poor parenting. By poor parenting I meanwell-intending parents whose behavior towards their children was never aimed at bringing out aggression in them. But the results are exactly that! There are various reasons why this can happen and they are different in every case.
There is a third common case in which parents bring their children to a therapist. In these cases the children have no issues whatsoever and it is the parents who see issues in their children. These are the cases of unrealistic expectations on their children where the parents often wish to exert too much control on their children. They want their children to obey every single command, to study for long hours, not to cry when beaten, to do this, and to be that! These parent exert too much pressure on their children and when the children reach their breaking point and react, the parents see that as an issue in their children not as poor parenting!
The above are three very common issues, but a parent may be (may be) responsible for the any kind issue in their child. Many issues in a child are a result of his circle of interaction and parents form a big part of that circle.