What....why?

My youngest child was born in 2000.  Let's be honest, she has no memory what so ever about 9/11. She has however reached the age where she understands what it means when some talks about it.  Well, I am not often caught off guard by anything the kids say to me, but 9/11 this I was.  

A third grader was checking out her book and when she turned to leave she said,

 

"Happy 9/11, Mrs. Honey"

I am sad to say that I had nothing to say back.  Very rarely am I left speechless, but that day I was.  I was so shocked I didn't even correct her before she made it out my door.