Reference: Fataawa wa Rasaa.il Mukhtaarah – Page 533
Question: Is it permissible to lie to a child of six years of age for his benefit and [also] to discipline him?
Response: Lying is not permissible; Not to the young and nor to the old. And if children are lied to, then they conceal [the truth], and if the adults lie, then the young learn from them and seek pleasure in it.
It has been mentioned on the authority of ‘Abdullaah ibn ‘Aamir (radhi-yAllaahu ‘anhu) that he said: My mother called me one day whilst the Messenger of Allaah was sitting in our house and she said: “Come here and I’ll give you (something)”. So the Messenger of Allaah (sal-Allaahu ‘alayhi wa sallam) said:
«And what did you want to give him?»
She said: “I want to give him a date”. So the Messenger of Allaah (sal-Allaahu ‘alayhi wa sallam) said to her:
«Certainly, if you do not give him anything, then it will be written that you told a lie» – transmitted by Ahmad, and Abu Daawood.
And with Allaah lies all success.