Is it permissible to dedicate a will to distribute an amount equal to the value of a previous gift given to one of the children, to the remaining children before the division of the inheritance after death, due to the inability to give it to them now?

It is not permissible to bequeath a gift to one of the children after death, because it is a bequest to an heir, and it is not executed unless the other heirs approve it. If you have gifted one of your children to the exclusion of others, you must rectify this by gifting the others similarly, or by deducting the value of the gift from the share of the gifted son from the inheritance if you pass away before rectification. You must strive to correct this during your lifetime.