Do you remember telling a lie at 2, 3, or 4? Well, feel guilty no more! Lying is actually a reliable sign of higher cognitive functioning. It was previously accepted that children were able to start lying at 3.5 years and no earlier. However, a recent study by psychologist Angela Evans found that 25% of two-year olds, 50% of three-year olds, and 80% of four-year olds were capable of lies.