"How is the child's answer?"
Translation:Câu trả lời của đứa trẻ như thế nào?
I'm confused by your question. Are you asking about the English or the Vietnamese sentence? (I feel the Vietnamese sentence is just a direct translation from the English.) Either way, the "how is" sentence is a broad question type that allows the speaker the freedom to answer as he/she wishes.
Now, when I throw in the towel and try:
"Đáp án của đứa trẻ như thế nào" (because DL seems to be marking all the 'làm sao' constructions wrong, contrary to what the course notes say) it now says "GOTCHA AGAIN!! WRONG AGAIN!!", the answer should be:
Đáp án của đứa trẻ thì thế nào?
Where'd the 'thì thế nào' come from? Of course, somehow, someway, we are expected to know this.