A child who promises you nothing will not lie, because he does not know what he is doing when he promises.However, if he backtracks, the situation is different. This is a retrospective mistake, because he clearly remembers his promise, but he does not understand the importance of keeping the promise.Since he can't look forward to the future, nor can he predict the consequences of things, even if he breaks his promise, there is nothing wrong with all the reason at his age.