Okay, so there was a story a long, long time ago about a mean guy named King Herod. King Herod was very jealous and didn't want anyone to take his place as king. One day, some people told him that there was a baby boy born who was supposed to be the new king. This made Herod very scared that he would lose his power.
In order to make sure he stayed king, Herod ordered his soldiers to go around and kill all the baby boys who were born around the same time as this new baby boy. This was called the massacre of the innocents.
It was a very sad and scary time for the families who lost their babies. But luckily, the new baby boy who Herod was so afraid of, had parents who were warned in a dream to flee to safety. They were able to escape Herod's evil plan and the baby boy grew up to become a very important person named Jesus.
So, in summary, the massacre of the innocents was a terrible event where a king ordered his soldiers to kill all the baby boys in order to keep his power. But one baby boy was able to escape and grow up to make a big impact on the world.