young children start to learn to lie as they mature cognitively and socially. In order to lie, children have to understand that other people have their own beliefs and thoughts that are not the same as theirs. A child also has to realize that other people may believe things that are wrong. this is a skill called theory of mind and it develops slowly in the preschool and kindergarten years. As children become more able to think about what other people think and feel, they learn when it's appropriate to lie and how to lie convincingly.