Yes. A family loan may be granted without interest, but in all cases, it must be repaid. It is advisable to put it in writing (French Civil Code, Art. 1376) and, for greater legal and tax security, to have it drawn up by a notary.
Please note when the total amount of the loan or loans granted over the course of a year exceeds €5,000, it must be declared to the tax authorities using CERFA form No. 2062 at the same time as the income tax return.