Do you hear yourself? You are saying that a child should be killed just in case they might have a less than optimal childhood. Did you know there is an adoption waiting list for newborns? So even if their birth mothers do not want them, someone else does.
And just because someone can’t know they are unwanted or think that they did something wrong is no justification for killing them. If it were, we could begin to slaughter entire groups of the mentally ill and the elderly.
If death is your answer to helping children live a better life, then you need to reevaluate your philosophy.