Youd need to view the entire rejection to know which dependent its referring to (highlight the client file, hit F12 and choose rejected Returns and print the report), but do any of the kids have double middle or double last names?  

Sometimes the name you have last isnt what IRS has a last and the name and SSN dont match.

 Ask for the actual SS cards to tell which name is really "last", it will be on the second line of the SS Card.