Passing Customer Name to Custom Record

I have created a custom record that is a child record of a Customer. I am trying to create a workflow such that when a custom field is completed on the Customer record, a new child record is created. I'd like a field on the child record to be autopopulated with the name of the parent customer, however, I cannot figure out how to do this. The workflow creates the child record and populates a date field from the parent record correctly, but the customer field on the child record remains blank. I've made sure the field on the child