Found by Margaret Peterson Haddix

It wasn’t there.  Then it was.  Later, that was how Angela DuPre would describe the airplane—over and over, to one investigator after another—until she was told to never speak of it again.  The mysterious airplane arrived at gate 2B carrying only 36 babies, one on each seat.  13 years later, Jonah, one of the adopted babies, receives a letter in the mail with only six words on it.  You are one of the missing.