Much of the fundamental ideas of Piaget’s work were based on his intense, methodical observations of his own three children, Jacqueline, Laurent, and Lucienne. Their mother was a trained psychologist herself and helped in these studies. In fact, she had been one of Piaget’s students. Although we can question what emotional impact this intense attention may have had on these children, Piaget’s investigations were never invasive or even particularly experimental. Relying on a naturalistic approach, for the most part he observed their natural behavior, questioned them about their understanding of natural events, or minimally modified their environment, for example by manipulating toys.