I gave an apartment to my daughter, who has three children. If she dies before me, the notary tells me it's possible to get it back. Is this true?

Yes. Everything depends on how you draft your deed of gift. If nothing has been stipulated, as the gift is irrevocable, the law does not allow you to recover your property. On the other hand, if a "conventional return clause" has been provided for in the event of the predecease of the donee (in this case, your daughter), with or without posterity, then you will be able to recover the donated property.