I want to give bare ownership of assets to my minor grandchildren and keep the usufruct. If I die before they reach majority, I do not want these assets to be managed by their parents. Is this possible ?

Yes. It is entirely possible to make a donation to your minor grandchildren. This donation must be accepted by their legal administrators (their parents), in accordance with Article 935 of the Civil Code. However, you can specify in the donation act that the donated assets be managed by a third party.