Toddlers and preschoolers often do so out loud, but kids don't stop when they get older, the researchers said. Instead, they tend do so in silence -- it helps them express their inner world, enliven play and regulate behavior.Other studies have shown that engaging in "positive self-talk" can improve children's performance in sports such as handball, soccer and swimming. Research has also shown that children who engage in self-talk that emphasizes incompetence, failure and personal harm experience more anxiety and depression, the study said.The researchers said when it came to math, the self-talk removed a "psychological barrier" that otherwise hindered performance -- they found no evidence that this approach benefited children who already performed up to their potential."When children with negative competence beliefs work on mathematics problems, they are prone to anticipate and worry about failure. They experience challenge (e.g., a difficult problem to solve) as a signal that they lack ability, triggering disengagement from the task and worsening performance," the study said."Effort self-talk may counter this process ... Children shift their attention away from their perceived (lack of) ability — a quality that is beyond their control — toward a quality that they can control: investing effort."