Can i create a button on parent request to create child requests ?
Is this in Service Catalog / Desk context?
What is the business requirement driving this, maybe some of that background will help other members to offer some ideas.
Ian, somewhere in detail_cr.htmpl custom file(you would need to decide where to put it), add this statement:
<PDM_MACRO name=button caption="Add Children[*Q]" endrow=yes func="update_child('cr', '$args.persistent_id', 'children', 'cr', 'parent', 'Requests', 'Request $args.ref_num<BR>Children')" hotkey_name="Update Children[*Q]" id=UPDATE_CHILDREN newrow=yes>
newrow=yes is option...it depends if you want to have a new row here.
And follow the standard process to save the change, pdm_webcache -H, clear browser cache and you will see the button "Add Children".