Child table updates and triggers an email from Parent table

This,  would be easy to do with a Pipeline.  On the parent record, you could have a Checkbox field, which when change would trigger an email notification.  Then you could have a Formula Field on the Parent Rykert, which would be the opposite of that Checkbox field.  

The formula would be. 

not [my check box field]

The pipeline would trigger when a child record is added it within the next step would be to look up the parent record, I think that step is called Fetch record, and then the step after that would be to change the checkbox field to the value in the field opposite checkbox field