Karma

[Coordinate_Apotheosis]

I think a child dies horribly in an accident because that was part of their life plan that they and their guides designed before they came into this life. I don't think that's karma.

I think negative people use negative karma to their advantage. Our hell would be their heaven.

Why would that be a life plan? how's that helping anything?
And what is negative karma?

The books by Michael Newton, such as Journey of Souls, or Destiny of Souls, describe a few examples of souls reincarnating into a life that they are aware of will come to an end early on.  They take on this role as a form of catalyst to the parents was one example given, in that the parents needed the karma of a child being born then dying early to them, and another soul is willing to take up the role of the child.

Then there's as apw said, probabilities.  Sometimes there's the chance that the 3D world will knock a soul out of an incarnation.  Michael Newton's work recalled one such instance of a soul who was killed in an accident before their planned time of death.  They were extremely unhappy with it, but had to accept it all the same.

So, when a child is born, and dies soon after.  There's some purpose and reasoning behind it, that to very many will look like a cruelty of an apathetic indifferent universe.  I know I see it that way still despite the above knowledge, and yet we are given some insight from others like Michael Newton and his works as to why this might happen, and why it doesn't mean the universe is apathetic and indifferent, but closer to methodical.