Can parent Child relationships be sert up for service requests-  like incident request parent - child?  or can it only be done with templates in service requests

I am afraid that's not possible. You can however create a related item to bind all SR to a "parent" and for example if you want to autoclose all related objects when the "parent" is closed that's possible with orchestrator and powershell. 

Thanks for the reply - is there a link with more detail that you could direct me to?

I don't think i have seen a post about this, i know it can be done but i can't explain in detail here on how to do it. To sum it up

1. Orchestrator looks for Service Requests that changed status completed. And perhaps we have extended the class with a new property auto close related items. So the runbook only runs if those criteria are met. 

2. When the runbook trigger we get all the related SR and close them and add a nice comment like closed by parent SR2222 

It's not that hard but you have to do some googling on the Orchestrator activities and how to extend the SR class/form with the autoclose.