At this time if you are editing a parent row with child items you cannot delete a child. Not sure why it behaves like this. When you are adding a parent row with child items you can remove at this stage but once you save the parent and then edit, the Delete option for child items is replaced with Cancel.
I know you can delete child items in parent detail view but the problem is if you have values in parent row calculated by child values, deleting a child wont update the parent value. This can be achieved if you edit the parent(form mode) and then delete the child items.
This feature is really helpful for me and i hope for many others. Is this a hard thing to implement? I kinda need this as soon as possible.