OK - I'm going to actually do this as I record it, so that I can be clear. I'm adding a "child", so I've opened that new child window...
Filled in all the field data above. And went to the last 2 boxes.
Now for the Notes box, I like to put some general biographical notes to help me remember who I put in there, and how they are related. So, for example, I'm entering (in the Notes): Son of Henry Mitchell and Amanda Guyton. (hit enter 2x) Husband of Emma Jane Anderson
Then, I go to the Sources box. (and of course, my sources are off-line - grrr... ), well, in this case, I'll put the LDS URL for the profile:
https://familysearch.org/tree/person/LT3M-Z36/details?parents=LT3M-8L7_LT3M-HQX
I then click the ADD button.
https://www.wikitree.com/wiki/Mitchell-16446
And no "Unsourced" there. I'm wondering if you don't put anything in the Notes box, then it also adds the "Unsourced" template?