Exo 30:11-14
11And the LORD spake unto Moses, saying,
12When thou takest the sum of the children of Israel after their number, then shall they give every man a ransom for his soul unto the LORD, when thou numberest them; that there be no plague among them, when thou numberest them....
...14 Every one that passeth among them that are numbered, from twenty years old and above, shall give an offering unto the LORD.
Exo 14:29-30
29 Your carcases shall fall in this wilderness; and all that were numbered of you, according to your whole number, from twenty years old and upward, which have murmured against me,
30 Doubtless ye shall not come into the land, concerning which I sware to make you dwell therein, save Caleb the son of Jephunneh, and Joshua the son of Nun.
And refering to David and Bathsheba's son who God took to heaven shortly after his birth. David is looking forward to meeting his son in heaven in the future.
2 Sam 12:23
23 But now he is dead, wherefore should I fast? can I bring him back again? I shall go to him, but he shall not return to me.
God is longsuffering, becoming twenty years old appears to be a landmark age n the scripture. Do a search on twenty to see how many references there are regarding that age.
If children are either born innocent or not held accountable for their sin, then why do children die?
If you can prove it has anything to do with the New Covenant, go ahead.
Twenty years old was representative of all of old Israelites who died off, and were told they could not go into promised land. The sum of their children, meant to count them.