Which group of mammals is characterized by young that are nourished in a pouch until they are more developed?

Marsupials are a distinct group of mammals that give birth to relatively undeveloped young, which then continue to grow and develop inside a pouch on the mother's body. This adaptation allows for a unique method of nurturing, where the young are provided with protection, warmth, and access to the mother’s milk as they mature. While monotremes lay eggs, and eutherians (or placentals) nourish their developing young through a complex placenta before birth, marsupials differentiate themselves by this pouch-nurture system. This feature is crucial for their development, as it allows them to be born at an earlier stage of development compared to other mammals, providing a flexible reproductive strategy suited to various environmental conditions.