speaking lie--The habit in children?

I actually think it is part a memory problem and part "wish fulfillment". Most children, until their adolescence, are basically impulsive and are more likely to seek to fulfill their desires rather than delay gratification for something better or because they see the "justice" of it. Frontal lobe functions, otherwise known as executive functions, are the last to develop. Sometimes they are not developed in adults. Delay of gratification is one of the behaviors that most reliably shows mature intellectual functioning.