Perhaps I am not making myself clear. It has been claimed young children do not and cannot do anything wrong. That claim contradicts the facts of reality. Children do things wrong all the time, every day, all day long. Likewise, the argument has been made they are not responsible or culpable but both responsibility and culpability are irrelevant if no wrong has been done. In other words, merely by arguing against responsibility and culpability the wrongdoing has been implicitly acknowledged. There'd be nothing for which to hold them responsible or culpable of nothing had happened. So, the minute either of you guys assert the premise of culpability you've contradicted yourselves! It cannot be said "now wrong is possible," and then argued, "There's no culpability." Then there is the problem of using earthly legal jurisprudence as an analogy for sin. It's a flawed analogy. It's built on the premise some law and its legal system are the only means of identifying sin and that premise is not scriptural. 1 John 3:4 is not the only verse in the Bible that defines sin and, as has already been demonstrated, sin existed prior to the giving of the Law of Moses. There'd be no talk of accountability if it did not exist! Then there's the matter of disciplining children. Either children did, in fact, do something wrong and are therefore in need of correction, training, rebuke, and discipline, or there is no warrant or need for ever disciplining any child. On every occasion when a no-sinful-kids person even admonishes a child with a single word they have contradicted themselves.
So, once again, there are many flaws, not just a single flaw, in this idea children are not sinful. Add all those flaws to the list I posted earlier, and the premise being argued became more untenable, not more viable.