First off, let me say that this is absolutely crazy, especially if she didn't learn it in class. I guess either the teacher wants the parent to do the homework for the child or the teacher wants to get out of a job and have the parent teach the child or the teacher thinks a six year old can look this stuff up on the net.
Here is the definition of a mammal from dictionary.com.
any vertebrate of the class Mammalia, having the body more or less covered with hair, nourishing the young with milk from the mammary glands, and, with the exception of the egg-laying monotremes, giving birth to live young.
Here is the definition of monotreme which makes this all the more confusing.
any animal of the Monotremata, the most primitive order of mammals, characterized by certain birdlike and reptilian features, as hatching young from eggs, and having a single opening for the digestive, urinary, and genital organs, comprising only the duckbill and the echidnas of Australia and New Guinea.
