Who, why, what is an elect baby???
Good question,
Without sin in the world,there would be no death.
Sin has tragically changed the world, and death by sin.
God was not surprised by the sin of Adam.
Before the world was created God purposed to save a multitude of fallen sinners in union with His Son.
Jn 6:37-44,Hebrews2:11-16.
We all have an appointed time of death
HEB9:27.even infants,so those who wrote the 1689 confession of faith wisely wrote that;
All elect infants dying in infancy would be saved by the working of the Spirit,which is unseen
That answers the question totally as it leaves it 100% up to God and His Holy wisdom, and omniscience.
In other words, if God has elected all infants who die that is His will.
If God has elected147 million infants who die, He alone knows why.
If he did not elect any, He would have a reason.
Many want to speculate and say God would not, or could not do this or that.
I do not speculate, but leave it to God as the confession of faith does. Gen 18:25
So elect infants would be those who were given by the Father to the Son.