Given scene/plot descriptions from movies or TV shows, and given a specific question about the scene, summarize the question into a title

In Game Of Thrones Season 4, the wildling Craster leaves his sons, from his wives (at the same time his daughters), into the woods to be taken by the White Walkers' king, after that he turned them into new White Walkers. I tried to figure out the reason behind this event, but no clues.  So, What is the story behind this action? And why does the White Walkers' king need those new born babies?
Why does Craster give those sacrifices to the White Walkers?

In Patriots Day, Dun Meng is video calling to his parents about his new vehicle. (This happens at the beginning of the movie).      The terrorist hijack his vehicle later.  The next victim, this cute couple appeared on screen even before the attacks.    After the attacks, this couples lost their legs in the terrorist attacks.  What is the significance of showing the victims even before the attacks?
What is the significance of showing victims even before the attacks?

In Kindergarten Cop (1990), why are there kids above 6 learning inside a normal school? Are they special, or is something off? For example, the bad guy is searching a kindergarten for his kid, while stating his age is 6.

Why are there kids above 6 and in school