Field empty calculation

[Koonce]

I have a field that I want to populate only if one thing is present. but I want it to populate with the following criteria. If the child's last name is different than the parents then I want the field to be the childs first name and his last name, if it is the same then I want to use the childs first name and then the Last Name field. Now is there is no child first name that is populated then I don't need anything to happen.

What I did works except when there is no child first name. It will populate with the last name anyway.

The Childs First Name, and if

Case (Child 1 Last If Different > 0;Child 1 & " " & Child 1 Last If Different;Child 1 & " " & Last Name

)

Thanks in advance.

[Fitch]

case(

IsEmpty( Childs First Name ) ; "" ;

not IsEmpty(Child 1 Last If Different ) ; Child 1 & " " & Child 1 Last If Different ;

Child 1 & " " & Last Name

)