Are children sinful for taking money in excess of their personal needs from parents who are spending on their studies, under the pretext of providing for their own private needs, knowing that the parents are not stingy but rather careful in their spending?

If the father spends on his son what is sufficient for his obligatory maintenance, then it is not permissible for the son to take more of his money except with his knowledge and consent. Lying to obtain money leads to two forbidden acts: lying and consuming unlawful wealth, both of which are destructive sins. The Prophet, peace and blessings be upon him, said: «Beware of lying, for lying leads to immorality, and immorality leads to the Hellfire.» And regarding unlawful wealth, he said: «Indeed, your blood, your wealth, and your honor are sacred among you.»

The Prophet's permission to Hind to take what suffices her and her child from Abu Sufyan’s money was because he was not providing them with what was sufficient. If a parent spends on his child and frees him from the need to work, this is a blessing that necessitates gratitude, because working at this age can be exhausting and may jeopardize significant interests, such as a student's studies.