Can't see any difference between what I typed (except for accent marks, etc.) and the correct answer, but it was marked wrong. I typed "tα παιδιa τους εiναι αγoρια. Other answers to other challenges without the marks are marked correct, but with typos noted. Are the marks sometimes required to obtain a correct answer?
You are correct as far as what you see in my comment above, but that's my mistake here. In the lesson it was typed correctly and the word "τουσ"was flagged. I now know that it has to do with my error of using the "σ"character rather than the terminal "ς". Thank you for your help.