It is not permissible to take one’s father’s wealth without his consent
Question

                Before Allah guided me, I used to ask my father for money for private lessons. The cost would be, for example, 500, but I would ask for more, namely 600, and I would take the extra 100 to buy cards for my mobile phone and other things. Now, praise be to Allah, I have repented and stopped doing this. My question is: do I have to tell my father what I did and ask him to forgive me? Do I have to return this money to him when I get a job and start earning, or not?
Praise be to Allah.What you did of taking money from your father without his consent is not permissible, because the Prophet (blessings and peace of Allah be upon him) said: “It is not permissible to take the wealth of a Muslim except with his consent.” Narrated by Abu Ya‘la and others; classed as saheeh by al-Albaani in Saheeh al-Jaami‘ (7662).
The son has no right to take anything from his father’s wealth beyond what the father is reasonably required to spend on his maintenance, if the father is obliged to spend on his son’s maintenance because the son is poor.
The scholar Ibn Muflih said in al-Furoo‘ (5/595): He – that is, the father – is obliged to spend on his son in reasonable terms for what he needs of maintenance, or some of it, and to provide clothing and shelter, if his children are poor. End quote.
Now you have two choices:

Telling your father what you did, and he will either forgive you or ask you to pay back the money, and he has the right to do that.
Not telling him, especially if you fear that this will cause trouble, such as a dispute or conflict between you and your father, or his loss of trust in you. In that case, you must return the money to him, but it is not essential for you to inform him of that; rather the aim is to return the money to him by any means. Please see the answer to question no. 31234.

The scholars of the Permanent Committee for Iftaa’ were asked about the son taking from his father’s wealth more than the maintenance that the father allowed him to take as needed.
They replied: You must return what you saved of money that you took from your father for maintenance, because he allowed you to take according to household needs, but anything surplus that is not included in the permission he gave, so it is not permissible for you.
End quote from Fataawa al-Lajnah ad-Daa’imah li’l-Iftaa’ (21/175)
And Allah knows best.