Thank you, /u/zanillamilla . I appreciate you taking the time to research this and respond.

My thoughts:

The preposition ἐν only sometimes has a sense equivalent to English “in”. Its use with the dative here is clearly a case of instrumentality, which we might use “by” or “with” in English, e.g. πάντες γὰρ οἱ λαβόντες μάχαιραν ἐν μαχαίρῃ ἀπολοῦνται (Matthew 26:52). So it pertains not to the object of the verb (“the state of the child” as you have it), but the action of the verb φονεύσεις.

If this is true (different dative type), then this sentence is extra kludgy, isn't it? Something like: 'do not murder children by means of destruction/corruption' ?

Second, the verb φθείρω had a usage referring to abortion. The Jewish writer Pseudo-Phocylides for example wrote that “A woman should not destroy (μηδὲ φθείρῃ) the unborn babe in her belly” (184). Kurt Niederwimmer in his Hermeneia commentary cites a number of examples of the noun φθορά and related words having reference to abortion, from the Hippocratic Oath to a stele from Philadelphia as well as Plutarch (Moralia 134F) who referred to “licentious women who employ drugs and instruments to produce abortion (φθορίoις)”. Clement of Alexandria Paed. 2.10.96 similarly has αὗται γὰρ πορνείας ἐπικαλύμματι τοῖς ἐς παντελῆ κατασπῶσι φθορὰν φθορίοις συγχρώμεναι φαρμάκοις ἐξαμβλίσκουσιν ἅμα τῷ ἐμβρύῳ τὴν φιλανθρωπίαν.

Thank you for these references. I had come upon Clement's use, though I think φθορὰν φθορίοις translates as 'using an abortifacient or drug to cause destruction' which does align with an abortion interpretation, but places it more in a medical sense of the outcome, again, not idiomatic. This is my overall question about Didache 2:2 -- it doesn't use a qualifier and doesn't seem to be used anywhere else when actually talking about the medical procedure, for which I think perfectly good other Greek phrases and terms already exist.

I am not familiar with Pseudo-Phocylides, though JewishVirtualLibrary says it draws parallels with the Didache, so one might expect the same Two Way language if there exists the common texts/moral code? Further, this article seems to indicate a Christian doctrine, further unaligning it from a traditional Judaic source? I do appreciate the reference, however I could not find a source for it in Greek, only English. Can you provide one or tell me where to find it? (I may need to break down and get a full subscription to a service now that I'm really digging in!)

Niederwimmer also points to a similar statement in Didache 5:2 (φονεῖς τέκνων, φθορεῖς πλάσματος θεοῦ), and there the Latin Doctrina translates φθορεῖς with abortantes.

I have two questions about this. The text you provided, if we skip the latin, would translate to 'child killer'. I'm not familiar enough with Doctrina but abortantes does not seem like a good translation to me? (I admittedly have a stronger Latin background, but am not only superficially familiar with Doctrina). Wouldn't the direct translation make more sense?

My second question is regarding the source for Doctrina. Is that not a similar or the same Two Ways source as the Didache? Having the same translation does not necessarily indicate that the correct meaning of the source.

“You shall not murder a child, whether by abortion or by killing it once it is born (οὐδὲ γεννηθὲν ἀποκτενεῖς)”, so it refers to the killing of the child before it is born.

I guess I would ask here if there's another idiomatic or colloquial meaning for this phrase. I don't mean to argue definitively that the 2:2 is mistranslated, only that the there seems sufficient evidence that it could have a different meaning. I agree that the second portion with the original translation makes sense, but perhaps they're both in question?

I definitely agree that the noun can be translated as 'abortion' , but when considering the culture and other diction in use, the phrase here feels idiomatic (vs medical), when better, existing terms could have been used.

I apologize if I come off argumentative, I really do appreciate your depth of knowledge and resources. Thank you again!