When saying Havdalah during the nine days [Motzei Shabbos Chazon] one is to give the wine to drink to a child [whether male or female, although some rule only male] which has reached the age of Chinuch [of blessings although some say also Chinuch of Havdalah] but has not yet reached the age of Chinuch for mourning. If such a child is not available he may drink the [entire] Havdalah wine himself as usual.
 Rama 551/10
Other Opinions: Some Poskim rule one is to drink the wine himself by Havdala and is not required to give it to a child. [Michaber 551/10] This is the Sefaradi custom. [Kaf Hachaim 551/152; Leket Yosher p. 210 that so did Terumos Hadeshen; Siddur Yaavetz; Darkei Chaim Veshalom 668] Some Poskim rule one is not to say Havdala over wine but rather over beer although some are accustomed to drink wine. [Aruch Hashulchan 551/26] See Hiskashrus on the nine days for a story recorded of the Rebbe that he told the person saying Havdala to give the wine to a child.
 Based on 190/4
 Based on 295/4 that only one who fulfills their Havdala obligation may drink the wine, and women and girls are disputed in whether they are obligated in Havdala.
 Based on 190/4
 Kitzur Halachos 295 footnote 5 based on 295/4 that only one who fulfills their Havdala obligation may drink the wine. Vetzaruch Iyun Gadol on their ruling, as explained in previous footnotes.
 M”A 551/31. This means the child is not yet old enough to understand the mourning period.
 Even if it is more than a Revius. [Piskeiy Teshuvos 551/35]
 Rama ibid