Update Child Records Workflow

Hi, 

Is there any way of Updating a number of child Records with a Workflow? 

e.g. I have a Field on an Account Record that, when changed, I want to update a Field on all child 'Custom Address' Records. 

When you create the Workflow from the parent you have no access to update child Records, and when tried from the child it can be set up, but there's no way to trigger the workflow based on the parent.