Adam Clarke on Esther 8:11

To destroy, to slay, and to cause to perish - The same words as in Haman's decree: therefore the Jews had as much authority to slay their enemies, as their enemies had to slay them.

Little ones and women - This was the ordinary custom, to destroy the whole family of those convicted of great crimes; and whether this was right or wrong, it was the custom of the people, and according to the laws. Besides, as this edict was to give the Jews the same power against their enemies as they had by the former decree against them, and the women and children were there included; consequently they must be included here.