Identifying Piaget's Concrete Operational Stage

During the early stages of cognitive development, children undergo various transformations in their thinking abilities, as described in Jean Piaget's stages of cognitive development. One of these stages is characterized by children beginning to think logically about concrete events, but they still struggle with abstract or hypothetical concepts. At this stage, children also exhibit the ability to understand the concept of conservation, which refers to the understanding that quantity does not change even when its shape does. With this context in mind, which stage of cognitive development is identified by these specific characteristics?