Here's an answer to the FAQ "Why did Walter kill Brock?" regarding the TV show Breaking Bad. Please rewrite this in a way a non-fan would understand (meaning, a person who does not know the characters).

Walt literally had no other choice. Walt had destroyed his good relationship with Gus by saving Jesse's life from those two drug dealers and now as a result Gus was going to have him, Jesse, Hank, Skyler, Junior and Holly all killed. To make matters worse Jesse returned the favor by palling up with Gus (a child killer BTW). Since Jesse refused to help Walt save his family Walt had to find a way to get Jesse back on his side so that they could kill Gus and giving Brock a tummy ache was the only option he had left, thanks to Jesse.
Walt, the main character, was in a challenging situation where he felt he had limited choices. He had done something to upset his boss, Gus, by saving his partner named Jesse from harm. As a result, Gus wanted to harm not only Walt but also some other people close to him. To make things worse, Jesse started to side with Gus, who had a troubling history. Since Jesse refused to help Walt protect his family, Walt felt he had to find a way to regain Jesse's support. Unfortunately, he thought causing Brock, the six-year-old son of Jesse's girlfriend, Andrea, to become sick was the only option he had left, thanks to Jesse.