All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Taking the father's money without his permission is forbidden for a son as it is forbidden to take one's brothers' money unless they allow him. Allaah Says (which means): {And do not consume one another’s wealth unjustly}[Quran 2:188].
The Prophet said: "Taking a person's money without his consent is not permissible." [Ahmad]
Therefore, it is not allowed for a person to take the money of his father or brothers without having their permission.
He has to repent to Allaah and has to give the owners back what he took from them. The real cure form this bad habit could be possible after knowing its reasons.
The reason might be that the son is surrounded with bad friends who are addict to drugs and dissoluteness. He may need huge money to satisfy his forbidden desires and whenever he falls short of money he gets it using all possible means even through stealing.
The father should be aware of his child's whereabouts and should know about his friends. The Prophet said: "A man follows the religion of his friend; so each one should watch whom he befriends." [Ahmad and Abu Daawood]
There is no harm to let the child know that you know about his stealing and to enquire the reasons. Eliminating this habit might not be possible except after knowing the reasons of that bad practice.
We ask Allaah to guide all to what pleases him.
For importance we refer you to Fatwa: 86405 about living in non-Muslim countries, Fatwa: 81223 about paying back stolen money to its real owner and the Fatwa: 88293 about the limits of relationship with non-Muslims.
Allaah Knows best.