The fate of aborted babies
Can we say for sure, or not, that aborted babies go to heaven? Jeremiah 19 says the children sacrificed were innocent. In Mark 10 Jesus blesses the little ones. I am not aware of Jesus ever blessing anyone not in His kingdom. Yet, Psalm 51 says we are sinful at conception. Can a baby be sinful and innocent at the same time?
In the Bible God does not specifically address your first question. If he has not spoken, we cannot speak for him. We know what God says in the Bible: people are sinful and have a need for forgiveness. Your reference to Psalm 51 addresses that. God also explains in the Bible that he is both just and forgiving (Exodus 34:6-7). God declares that faith saves and unbelief condemns (Mark 16:16). He reveals to us what means he uses to create faith in a person’s heart. When we look at God’s revealed will to us and cannot find answers to our questions (like the one you posed), we bow in humble reverence to God (Romans 11:33-36) and leave unborn children in the hands of a wise, loving God whose ways are perfect (2 Samuel 22:31).
Just for the sake of clarification, the “innocent” in Jeremiah 19 refers to people who, through no fault of their own, were sacrificed in idolatrous worship. Their description does not pertain to a natural spiritual condition of some kind. We speak of “innocent” victims today: people who lose their lives through someone else’s violent actions, for example.
You may not have this in mind with your last question, but a baptized baby is sinful and innocent at the same time (so are the child’s Christian parents). We are sinners and saints in the eyes of God.
Your question about abortion is a reminder for Christians to “Speak up for those who cannot speak for themselves” (Proverbs 31:8) and to testify that life is a precious gift from God, who alone has the right to end life (Deuteronomy 32:39). You will find much good information on this topic from Christian Life Resources, an agency within WELS.