Yep, that will ceratinly work since calling the save on the form just calls the save on each business object that is a member of that form. However, just to clear up some confusion, calling the save on the parent will not automatically save the child. It will propogate the parent's new PK (if there is a new PK) to the child's foreign key field so that when it is saved everything will line up correctly.
If you call the save on the child, it will call the save on the parent if the parent IsDirty. So if you modify an existing parent record, or if you are working in a new parent record (the record will be dirty until it is saved the first time) then it will automatically call the save, otherwise it won't since it doesn't need to.