"You may feel singled out when adversity enters your life. You shake your head and wonder, 'Why me?' But the dial on the wheel of sorrow eventually points to each of us. At one time or another, everyone must experience sorrow. No one is exempt.... Sometimes the very moments that seem to overcome us with suffering are those that will ultimately suffer us to overcome.... The Lord compensates the faithful for every loss. That which is taken away from those who love the Lord will be added unto them in His own way. While it may not come at the time we desire, the faithful will know that every tear today will eventually be returned a hundredfold with tears of rejoicing and gratitude. One of the blessings of the gospel is the knowledge that when the curtain of death signals the end of our mortal lives, life will continue on the other side of the veil. There we will be given new opportunities. Not even death can take from us the eternal blessings promised by a loving Heavenly Father." (Joseph B. Wirthlin, Nov. 2008 Ensign).
One line is especially key: "The faithful will know that every tear today will eventually be returned a hundredfold with tears of rejoicing and gratitude." Our tears of sorrow will - sooner or later - turn to tears of joy. We don't always or even often understand some of the hard things we are asked to bear - and little could be harder to bear than the premature death of a child - but the Lord understands our pains. The Savior personally experienced them - all of them and more! He knows who we are personally and hears our prayers. He even matches our tears with His own.
The Prophet Joseph offered these words of faith to those suffering the pains and pangs of loss: "If I have no expectation of seeing my father, mother, brothers, sisters and friends again, my heart would burst in a moment, and I should go down to my grave. The expectation of seeing my friends in the morning of the resurrection cheers my soul and makes me bear up against the evils of life. It is like their taking a long journey, and on their return we meet them with increased joy." (Source). Sometimes that long journey into the eternities occurs early in life and sometimes it occurs late in life; but for all, it does occur.
Link to part 5 of this essay.