If their name was there it was there.. from before the foundation of the world.
Calvinists do not believe there is an age of 'accountably ' (as scripture never teaches such a thing...it is a throw back to RC doctrine and baptismal regeneration)
We believe that it is God that does all the work in salvation , so just as John leapt in the womb at the presence of Christ , Gods grace does not rely on age to acknowledge Him .
The majority of Calvinists ( like Calvin that lost a young child) believe that God saves all children that die. Not because they 'deserves' it based on innocence , but based like all of our salvation on His mercy and grace.
I am of the school that believes we can not ever know what God does until we stand in His presence. At that time no matter how he handles the death of a child , we will see it with as just and right
'Shall not the Judge of all the earth do right?' Gen. 18:25.
with the exception of 2, God only brought the under 20 crowd out of the wilderness. They weren't held accountable .
Why? Why would God save all children that die? Aren't they, according to the doctrine of total depravity, as deserving of hell as the most reprobate adult?