what a good children you are!

问题描述:

what a good children you are!
还是?
what good children you are!

当然是 What good children you are!(你们是多好的孩子啊!)
children 是复数,前面不可能用 a.
感叹句 What ... 后面可以用复数名词或不可数名词,又如:
What modern houses they are!
What lovely weather!