God tells us He determines the day we're born and the day we die...
Seeing his days are determined, the number of his months are with thee, thou hast appointed his bounds that he cannot pass" -- Job 14:5 "...(He) hath determined the times before appointed, and the bounds of their habitation" -- Acts 17:26"Thine eyes did see my substance, yet being unperfect; and in thy book all my members were written, which in continuance were fashioned, when as yet there was none of them." -- Psalm 139:16
Therefore, we must conclude God gives us our children for as long as He determines we shall have them.
The glorious comfort for the believer is that our children are a part of His convenant, the seed to whom the promise was made.
"They shall not labour in vain, nor bring forth for trouble; for they are the seed of the blessed of the LORD, and their offspring with them." -- Isaiah 65:23
Like David, we know we will see them again...
"I shall go to him, but he shall not return to me." -- 2 Samuel 12:23
The saddest, most unbearable pain in the world is losing a child. How do non-believers or those with no certain assurance cope? It must be dreadful.
What we know for certain is that God's election stands. I like what Warfied said concerning those who die in infancy...
And if death in infancy does depend on God's providence, it is assuredly God in His providence who selects this vast multitude to be made participants of His unconditional salvation... This is but to say that they are unconditionally predestinated to salvation from the foundation of the world. If only a single infant dying in irresponsible infancy be saved, the whole Arminian principle is traversed. If all infants dying such are saved, not only the majority of the saved, but doubtless the majority of the human race hitherto, have entered into life by a non-Arminian pathway.""Their destiny is determined irrespective of their choice, by an unconditional decree of God, suspended for its execution on no act of their own; and their salvation is wrought by an unconditional application of the grace of Christ to their souls, through the immediate and irresistible operation of the Holy Spirit prior to and apart from any action of their own proper wills...
As Warfield says, the salvation of even one infant proves the truth of God's perfect election, founded "not of him that willeth, nor of him that runneth, but of God that sheweth mercy" (Romans 9:16).
Praise God!!!