I know we are not accountable for our actions until we are 8 years old. What about that 6-year-old kid in Michigan who shot the girl in his class? If they would decide to execute him, would he automatically go to the Celestial Kingdom because he was a child, even though he committed murder, an unforgivable sin?
Little children cannot repent; wherefore, it is awful wickedness to deny the pure mercies of God unto them, for they are all alive in him because of his mercy.
For behold that all little children are alive in Christ, and also all they that are without the law. For the power of redemption cometh on all them that have no law; wherefore, he that is not condemned, or he that is under no condemnation, cannot repent; and unto such baptism availeth nothing (Moroni 8:19,22).
And I also beheld that all children who die before they arrive at the years of accountability are saved in the celestial kingdom of heaven (D&C 137:10).
The operative word in the above scriptures is the word ALL. The scriptures do not imply that little children cannot sin. If that were the case, there would be no need for the Savior’s atonement in their behalf. Although they can and do sin (since sin the the violation of the law) the power of the atonement paid the price to the demands of justice for their sins, so they are not charged. And if they die before the age of eight they are saved in the celestial kingdom of heaven.
In the case of the little boy that you refer to, even the courts of the land recognized that he was not accountable and was not charged.