The child can qualify the taxpayer for two different purposes.  One, filing status.  Two, child credit (and sometimes, childcare credit).  If the child is already listed for the credits, the listing for filing status is not required because it's already obvious that there is a qualifying child for filing status.  If the child is not listed for the child credit, because of a divorce agreement, then you list the name for filing status.  Happens all the time.