Give the key figures names of the 2^nd stage of psychology development

The key figures associated with the second stage of psychological development are Jean Piaget and his theory of cognitive development. Piaget proposed that children progress through four stages of cognitive development, with the second stage being the preoperational stage, which typically occurs between the ages of 2 and 7. During this stage, children begin to engage in symbolic play and develop the ability to think symbolically, but they still lack the ability to perform operations or reversible mental processes.