Stop asking questions and answer this one:
Do you have a scripture verse to back up your assertion that,
"God CAN cover the sinfulness of infants and challenged persons, by deciding to apply effectually the atoning death of Christ to their behalf!"
I am going to go with 1 John 2:2 And he is the propitiation for our sins: and not for ours only, but also for the whole world.
I would say he is the propitiation for the whole created system that came under the curse of sin both animate and inanimate and is the reason why Paul makes the following statement:
For I reckon that the sufferings of the present time [are] not worthy [to be compared] with the glory about to be revealed in us; for the earnest looking out of the creation doth expect the revelation of the sons of God; for to vanity was the creation made subject -- not of its will, but because of Him who did subject [it] -- in hope, that also the creation itself shall be set free from the servitude of the corruption to the liberty of the glory of the children of God; for we have known that all the creation doth groan together, and doth travail in pain together till now. And not only [so], but also we ourselves, having the first-fruit of the Spirit, we also ourselves in ourselves do groan, adoption expecting -- the redemption of our body; Romans 8:18-23
Lord, teach us to pray
When ye pray, say, Our Father which art in heaven, Hallowed be thy name. Thy kingdom come. Thy will be done, as in heaven, so in earth.
After this I will return, and will build again the tabernacle of David, which is fallen down; and I will build again the ruins thereof, and I will set it up:
That the residue of men might seek after the Lord,
and all the Gentiles, upon whom my name is called, saith the Lord, who doeth all these things.
And this gospel of the kingdom shall be preached in all the world
for a witness unto all nations; and then shall the end come.