जीन पियाजे के संज्ञानात्मक विकास के सिद्धांत के अनुसार, विकास की दूसरी अवस्था कौन सी है?

According to Piaget's theory of cognitive development, at which stage does the ability of 'conservation' begin to develop in a child?

Jean Piaget proposed that children's thinking is _______ that of adults.