Matteo 2:16

Then Herod, when he saw that he was mocked of the wise men, was exceeding wroth, and sent forth, and slew all the children that were in Bethlehem, and in all the coasts thereof, from two years old and under, according to the time which he had diligently enquired of the wise men.

The evangelist, after his brief digression, returns to his story proper. Herod saw that, from his standpoint, he had been outwitted, made a fool of, by the Magi. And when he was certain that they were not going to retrace their steps to Jerusalem, to report what they had found at Bethlehem, he was enraged, extremely incensed with an unreasonable rage. This wrath demanded an outlet, it could be quenched only in blood.

Herod sent executioners. to Bethlehem with the command to kill all children that were to be found in the village proper and in its entire vicinity, the rural district surrounding the town. Not one was spared, not even, according to an ancient report, his own son. In fixing the age of his victims, he made use of the information given him by the Magi, probably extending the time either way in order to make sure that none escaped. Herod would not be too scrupulous: from one hour to two years old, it mattered not; if anything, it insured him an ample margin either way