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 رضي الله عنه 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 ﷺ said:
«And what did you want to give him?»
She said: “I want to give him a date”. So the Messenger of Allaah ﷺ 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.
