What suckle their young?

Mammals.

Mammals are a diverse group of animals characterized by features such as mammary glands to feed their young with milk, hair or fur, three middle ear bones, and a four-chambered heart. The mammary glands, which produce milk, are present in all female mammals and function as the primary source of nutrition for their offspring during the early stages of their development. This characteristic of giving birth to young and nourishing them with milk is a critical aspect of mammal reproduction and maternal care. Various mammal species possess unique variations in their suckling behaviors and lactation periods, ranging from a few weeks to several months or even years in some cases.