When Jarrett J. Krosoczka was in high school, he was part of a program that sent students to be counselors at a camp for seriously ill kids and their families. Going into it, Jarrett was worried: Could anything he did make a difference? Wouldn't it be depressing to be around kids facing such a struggle? But instead of the shadow of death, Jarrett found something else at Camp Sunshine: the hope and determination that gets people through the most troubled...