Shaykh Uthaymeen رحمه الله said:
Its befitting that the children are taught the rulings (of affairs) with their evidences.
For example, if you want to teach your child by saying to him:
'Say: bismillaah (In the name of Allah) before eating and al-hamdulillah (all praise belongs to Allah) after finishing, then if you have said this, then the goal has been reached. However if you say:
'Say: bismillah before eating and alhamdulillah after finishing because the Prophet ﷺ commanded (us) to say bismillah when eating and alhamdulillah afterwards and the Prophet ﷺ said:
"O young boy say bismillah..." and this is (the proof) for saying bismillah.
And the Prophet ﷺ said:
"Indeed Allah is pleased when His servant eats and praises Allah afterwards and drinks and praises Allah afterwards"
So if you do this you have obtained two benefits:
1 - You have trained your child to follow the proofs
2 - You have cultivated the child with loving the Messenger and that he is the Imam to be followed which its binding to take his guidance and advice.
And this in reality many are heedless because most people direct their children to the rulings but does not connect the guidance to its source which is the Book (the Quran) and the Sunnah.
al-Qawlu al-Mufeed alaa kitaab at-Tawheed 2/423
Translated by Abu Anas Atif Hasan