Final answer:
According to Piaget, a 4-year-old child is in the preoperational stage where imagination is dominant; acknowledging their fears and providing security is better than explicitly denying the existence of monsters, which supports cognitive development.
Step-by-step explanation:
In the scenario where a 4-year-old child claims there are monsters under the bed, Jean Piaget's theory on cognitive development would suggest that at this preoperational stage, a child's thinking is still largely influenced by imagination and egocentrism. It is not uncommon for children of this age to have imaginary companions or fears, as their grasp on reality vs. fantasy is still developing. As such, it may not be entirely effective to simply teach the child that monsters don't exist. Instead, a parent should acknowledge the child's feelings and help them feel secure. This might involve checking under the bed together or providing reassurance. Punishing the child for their imagination would not be appropriate, as imagination is a natural and important aspect of cognitive development at this age.