Answer: The teacher should buy the same-sized glasses, as children at this age can't understand conservation.
Step-by-step explanation:
The understanding of conservation is the ability of a person to recognize that the amount of a substance does not depend on its content despite being able to adjust to various containers, that is if we have 1/2 liter of juice regardless of size or Container form the amount of juice will remain 1/2 liter.
However, the recognition of this implies a logical thought that is not yet developed in preschool children, it develops between 7 and 11 years, this according to the theory developed by the psychologist Jean Piaget.
I hope this information can help you.