Is it true that I am not entitled to claim the money I gave to my aunt with the intention of temporary assistance, knowing that it was my children's savings, on the pretext that I did not specify it as a debt due for repayment, and that she considers it assistance not requiring repayment, based on a sheikh's fatwa?

It is not permissible for you to lend your children's money to anyone, and you are accountable for it in all circumstances. If you gave the money to your aunt with the intention of a loan, and you did not utter a word signifying a gift, then you have the right to reclaim it. Your word takes precedence over hers in determining the intention, because the one who gives is most knowledgeable of their intention.