It is impossible to construct ethics from first principles.

You've never read Groundwork for a Metaphysics of Morals? That's pretty basic stuff, like Ethics 101 basic.

And I'm not even a huge Kant fan let alone a deontologist, in fact I'm more of a situationist, but you should at least be familiar with the Categorical Imperative before you make a nebulous claim like "A study of philosophy would tell you that."

Sometimes abstraction is good and necessary, but a statement like "There's no equation that can tell you it's a good thing for a child not to die of hunger" is an over-abstraction. There's no need to abstract it further, because the situation is already concrete. Anyone who has experienced grief can tell you that, and an ivory tower that's too sterile to taste grief has nothing to offer the world in the way of ethics.

Only a sociopath would have to wrestle with the question of whether there's anything objectively bad about children dying. Do you expect anyone to try to prove it mathematically? Because that would be entirely the wrong approach.

If you can't state "living is a good thing, and therefore premature loss of an innocent life is a bad thing" as a first principle, then there could be no point in debating ethics with you because you're already amoral.

I'm not accusing you of thinking that way, I understand you're presenting a line of reasoning in the abstract as a thought experiment. I'm simply telling you what my response would be to someone who tried actually arguing along that line.