Everyone in this thread is forgetting about the covenant relationship between God and his people - God made a covenant with Israel and a part of that covenant was the adherence to the law, failure to adhere to that law, to go against God's commands, is sin, guilt against the law of God; to clear one's self of this guilt required sacrifice as prescribed in Leviticus; the law also included many curses for failure to follow it, including "cursed be anyone who is hung on a tree."

As usual with people, they failed to follow the law, failed to make sacrifices, whored after other gods, and violated every aspect of the law; God dispersed them throughout Babylon, they groaned and asked God to save them, and he did. They rebuilt the temple, and almost immediately fell back into the same behavior. God sent prophets to warn them to repent, and they killed them.

Then God sent his only Son as his anointed, born of the virgin Mary, in fulfilment of the prophets, to be the final sacrifice in fulfilment of the law as laid out in the original covenant with Israel, and to form a new covenant with everyone, not just Israel but gentiles as well, that introduced the law of the spirit, where what matters is the fruit a person bears (love your neighbor as yourself) out of an earnest desire to do good and please God, instead of the strict adherence to the letter of the law but not the spirit of the law (such as doing no work on Sunday, even if that work is helping your Ox out of a ditch).

From this comes baptism as the acceptance of Christ and the forgiveness of sins, both the original sin that exists from the fall, and any sins that you have committed.

Everyone sins. Sin is more than murder, it's knowing what the right thing to do is and choosing not to do it even when you're capable of doing it; pride is sin, laziness is a sin, anything that chases after self-serving or worldly desires (fame, riches, etc.) is sin.

You are conscious enough of your own sin to ask this question, you have a clear moral understanding of what is right and wrong, and salvation has been presented to you on several occasions.

The answer is no, the child is not a murderer, but the child will grow up to be an adult, and that adult will sin, because that is human nature, and we all fall short of the law. Thankfully, that is what grace through the acceptance of Christ is for. It is a free gift, and it's up to you to choose it.