Final answer:
Children master different types of conservation problems at different ages based on their cognitive development stage, as theorized by Jean Piaget. The concrete operational stage is key to understanding conservation, while earlier stages show varying abilities such as object permanence and theory of mind.
Step-by-step explanation:
The concept that explains why children master different types of conservation problems at different ages is closely tied with the cognitive development theories of Jean Piaget. Piaget proposed distinct stages of cognitive development, one of which is the concrete operational stage, occurring from about 7 to 11 years old. During this period, children develop the ability to think logically about concrete events and begin to understand conservation: the idea that quantity or amount does not change when its form changes, such as recognizing that the amount of water remains the same when it is poured from one shaped container into another.
Before reaching the concrete operational stage, children go through the preoperational stage, where they might not yet grasp the concept of conservation. Cognitive abilities like object permanence and theory of mind (TOM) also develop at varying ages, which reflects the gradual nature of cognitive development. Piaget's theories have been refined by subsequent research, which suggests that children may have an understanding of physical properties and object mechanics earlier than Piaget estimated.
Stranger anxiety, for example, is a response that occurs when a child is unable to fit new experiences into existing schemas. This and Piaget's observation of toddlers in his conservation tasks offer valuable insights into cognitive development. The exact ages when children achieve certain developmental milestones can vary, highlighting the complexity and individuality of cognitive development.