Unsavable? No. Reprobate (left sinful, and thereby to suffer from their sinfulness, by the ordinance of God.)
Destroyed? No. Judged. With water. Next judgment will be with fire.
Geneses records that men who were destroyed
became unsavable starting with the falling away of the prophets who were responsible to speak to the people on Gods behalf.
In reading about Adams sin, we find that God shed blood over that and clothed them, so it was not because of Adams sin alone that men were destroyed in the flood.
The law was given in covenant from God to Adam so that man could choose to live a holy life according to God's moral standards. Adam did not believe the terms of this covenant, did not love God, and broke this covenant (as the federal head and representative of the human race). Hosea 6:7
No covenant existed at that time, only the giving of a command.
When little children or the intellectually impaired believe, it is because God in His grace has already regenerated them and raised them to life by the power of His Holy Spirit.
So you are saying God does not care about the children of Moslems.
Why does He not regenerate all of the children of all people so they can believe and save the world from a lot of trouble.
God does not have the character you think He has.
I suggest you put the teachings of Calvin aside and seek the Lord only.
Joh 12:32 And I, if I be lifted up from the earth, will draw all men unto me.
LA