Morals don't exist for an individual. They are a Collective. Just like particles interacting with the environment do so as a collective. Then they conform.
Morality and ethics are a collective. If you take any group you look at you cannot then look at it with you on it from an external force onto an inward one. You have to see how the people in the group feel and think . From the inside to the inside. If those people are feeling oppressed or hurt or they feel pain about this sacrificing of children then for that group it is not good. If no one in the group had any feelings or care about a sacrifice of a child, even the child itself then is it morally wrong for the group? If they were say robots with no care of their death? For them then that would not be immoral. But that is because morality is contingent upon the collective. Nature works as a collective.
I then came across this article which seems to think somewhat like I mentioned:
"Law instead follows from collective behavior, as do things that flow from it, such as logic and mathematics. The reason our minds can anticipate and master what the physical world does is not because we are geniuses but because nature facilitates understanding by organizing itself and generating law." -http://www.physicscentral.com/explore/writers/laughlin.cfm
I would add this law comes from the collective, how the parts work together and this is really how morals and ethics evolve as well.
Of course this is Laughlin who Kruass criticized, but I agree with Laughlin here.
As a mother Bonobo looks at her baby, she follows her instincts and her compassion and the level of teaching of care giving from her small community. She knows nothing of science. She is merely following her emotions and level of reason.
As an outside judgment of humans we can look at them and judge, but they are judgers of their own culture and own behavior. What they have deemed acceptable will pass and what is not will not in their group. That is their moral and ethic code.