Almost paradoxically, what can be most difficult in treating a child is not the child but their parents' resistance to their treatment which derives from misconceptions: that long-term problems can be eliminated quickly; that the therapist will try to control their lives; or simple jealousy, as when the child values their therapist, or a stuffed animal in their office: one child's tantrum immediately ended when his mother said they would visit "Donald" that day.
More difficult to deal with is parental guilt. While most children's problems do derive from inadequate early life parenting, this is never deliberate. Children do not come with instructions and possess variable parenting difficulty.
Moreover, parents had their own early experiences to survive and do their best. After engaging their child in therapy, any guilt which the parent feels is unwarranted.