Many thanks.
I'm close now (especially thanks to your tip about the spaces being vital).
The fields are now invisible if null but there is still a carriage return when the field is null (or zero).
The code I've got is:
Code:
{SKIPIF { MERGEFIELD Boy4 }="" }{ IF {MERGEFIELD Boy4 }<>""Boy Aged 4: {MERGEFIELD Boy4 }" "" }
Maybe I need to take the carriage returns out of the document and into the fields somehow.