For the sake of arguement, I would like to see one Bible verse, just one, that says that you need to be aware you are sinning for it to count as Sin.
again, I will quote -
Ezekiel 45:20 You are to do the same on the seventh day of the month for anyone who sins unintentionally or through ignorance; so you are to make atonement for the temple.
Numbers 15:28 And the Priest shall make atonement for the Soul that sinneth ignorantly, when he sinneth by ignorance before the lord, to make atonement for him. and it shall be forgiven him.
It is possible to SIN through IGNORANCE, or UNINTENTIONALLY.
Second, I would also like to see a verse within the Bible that says an individual is "Safe" until a specific age.
I will quote again;
Romans 3:23 for all have sinned and fall short of the glory of God
Romans 5:12 Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all men, because all sinned
1 John 1:10 If we claim we have not sinned, we make him out to be a liar and his word has no place in our lives.
1 John 5:4 for everyone born of God overcomes the world. This is the victory that has overcome the world, even our faith. 5 Who is it that overcomes the world? Only he who believes that Jesus is the Son of God
Proverbs 20:11 Even a child is known by his actions, by whether his conduct is pure and right.
Job 25:4 4 How then can a man be righteous before God? How can one born of woman be pure?
Ephesians 2:8 For it is by grace you have been saved, through faith—and this not from yourselves, it is the gift of God
Age of Accountability is not founded biblically, although is a comforting thought.
As for King David and his comment.
First, there is the debate as to how Sheol was divided before Christ, In fact it was possible for individuals to see each other across the divide, as is evident from the story of Abraham's Bossom. (which I would argue is not a parable.)
Second, the verse never claims the child is saved.
However, I will point out that God will do what is right, and just.
Romans 9:15 For He saith unto Moses, I will have Mercy on whom I will have Mercy, and I will have Compassion on whom I will have Compassion!
Don't assume that there is an age, or a mental requirement.
Live as though Jesus Christ is the only way to Heaven, and preach that he is the only way to be Saved. Take Comfort in the fact that God is Love.
Don't try and put rules and bounderies on Him that He has not explained through His Word.
God Bless.