(a) You are probably wrong, but the answer to this question requires some distinctions to be drawn.

The law does not impose a duty to prevent harm simply because that harm is foreseeable. And in many circumstances, no duty of care arises in respect of harm that may foreseeably result from a failure or omission to act.

But there are exceptions to this general rule. A duty of care may exist to prevent foreseeable harm when the risk of that harm has been created or increased by some act or conduct of the defendant, who will then be liable for failing to act to prevent that harm from occurring. It may also exist when the person who fails to act has previously assumed a responsibility, for example by undertaking a task, and the injured person relied on that task being carried out properly. An example of this would be if one person offered to look after another's child while the child played on the sidewalk. But in the case study, there is no antecedant act or assumption of responsibility, and A would not be under a duty of care towards the children.