Is it permissible to fill a private employee's car from the company's fuel card, designated for work vehicles, for personal use such as driving children to school, without the employer's knowledge, due to rising prices and insufficient salary to cover fuel costs?

Fuel cards are a trust, and they must be safeguarded and not disposed of except with the owner's permission. If the owner does not permit it, then it is not permissible to benefit from any of his property, otherwise, it would be consuming wealth unlawfully, as Allah Almighty says: "O you who have believed, do not consume one another's properties unlawfully but only [in lawful] trade by mutual consent from you." And as the Prophet, peace and blessings be upon him, said: "The wealth of a person is not lawful except with his willing consent."