Automation Modify vs new record

I have an automation that will trigger a new record in a separate table.  There are two scenarios where I want a new record created.  One is when a new record is created in the parent table and two is when a field changes from blank to being populated in the parent table.  I only want it to create a new record if a current record doesn't exist in the child table.  My issue I have is creating a work around that won't create a new record in the child table every time the field from the parent table changes.  I know I can add a step to the automation to update a field in the parent table that child table was created as a potential work around to filter the trigger but I wanted to see if there was an easier way.