Workflow - Create child Record

Hi, 

I'm trying to create a new child 'Custom Address' (custom entity) Record from a parent Account using an on-demand workflow.

I've essentially said: if Address 1: City / Street / Post Code contains data, then create a new Custom Address Record. 

The issue is, it's creating a child record without mapping any of the values over. It's just creating a record with the static values I've put in, leaving an orphan record. 

Any ideas?