We both believe in the sanctity of life. But I will play devils advocate for a minute. Why is this child’s life valuable? Simply because we say so? I hope there is a greater reason than that…
I appreciate that you are playing the Devil's Advocate, but might I suggest that life is such a capricious and unlikely occurence in the universe, that
ipso facto it is valuable.
Again, as the devil's advocate, I see no reason to regard life as an unlikely occurrence within the universe. It is no more or less likely than any other particular arrangement of atoms, quarks, etc. Yes we have the ability to reproduce. Yes, we have the ability to perceive. So what? We regress to a physical state and are nothing more than a compilation of molecules.
I suppose you could argue that if the universe never had a beginning, that life would inevitably happen; Life was doomed to happen. As such, why should I acknowledge the sanctity of life?
Within my (albeit subjective) morality, there is nothing - no transgression, no sin, and no circumstance which justifies the taking of human life. There does not have to be a reason, greater or lesser. It is axiomatic.

So the question here is not whether the parents have committed a crime, but why they did it, and whether such criminal acts may be justified by personal beliefs.
Why must they be justified? Who are/should they be accountable to?