---

@ChiHoang wrote:

My question is: can I file 2 of his children as dependents for child tax credit (CTC) for years 2021-2023?

---

They needed their Identification Number by the due date of the tax return.

That means for 2021 and 2022, no.  For 2023, if they filed an extension, yes.  If they did not file an extension, no.