Early death is only a penalty for people who lack faith in a life beyond this one. When you know that this life is just a chapter, you don't feel the need to prolong your "life" unnecessarily.
Do not mourn for the young dead, celebrate their return to heaven.
My daughter died at 20 months old from Hypoplastic Left Heart Syndrome. There is nothing to mourn. She's in heaven with the rest of my family and we can talk any time we want. This isn't an abstract hypothetical to me.
Karma means cause and effect. I never held my daughter because I left the state and broke up with her mom before she was born. I video called all the time, but I thought I had time, so I wanted to do the trip "right". Hindsight's 20/20, I could've made the trip by just buying a plane ticket and sleeping in a ditch for a weekend, but I didn't, so I never held her before she died. That's karma. That's cause and effect. My actions then led to my situation now.
Karma is a physical law, or rather, the culmination of physical laws. Understanding how the world works, how it will react to your actions, is understanding your own karma.
"Oh no, you flip burgers and believe in karma, you have a slave mentality!"
Oh no, you like eating burgers and I decide how closely to obey the hold timers in the cabinet. I guess that makes me the master of your lunch's destiny.