Muthsera,
The terrible and golden-hued "half-Elf", Umaril the Unfeathered was said to have the blood of the 'ada and would never know death. Umaril listed his bloodline in the Ayleidoon and spoke of his father, a god of the [previous kalpa's] World-River. (http://www.imperial-library.info/obbooks/songofpelinal.shtml)
Umaril has been linked to Meridia, and Meridia (a daughter of Magnus) is said to have been cast from the ranks of the Aedra due to consorting with "illicit spectra". (http://www.imperial-library.info/book_daedra/index1.shtml#meridia). It is quite possible that she "consorted" with Umaril's father, which resulted in the Unfeathered.
Thus, if such is true, we have a demonstration of cross-breeding Daedra.
But you asked if there were an example of a mortal offspring of a Daedra. The answer is yes, Nerevar is said to have been the son of Boethiah.
"This Nerevar is the son of Boethiah, one of the strongest Padomaics." (http://www.imperial-library.info/mwbooks/wulfharthsongs.shtml)
And we know what kind of mer this Indoril Nerevar was.
___TWM
I think the Nerevar being the son of Boethiah is figurative - Nerevar is more like the perfect catalyst for revolutionary change (the Tribunal) and murder (again the Tribunal murdering Nerevar), and betrayl (Vehk, Ayem, and Seht betraying their/Nerevar's oath to Azura). EDIT: also, the next line after the one you quoted: "He is a hero to his people despite his Tribunal, and he shall muster enough that this battle will be harder going still." Which is totally Boethiah's sphere. Maybe Nerevar is more a champion than an actual physical son of Boethiah?
As for the thing with Meridia, seems more like some sort of sorcery - maybe manipulation of the creatia that would become Umaril to give him Daedric properties? Or meddling with his soul/the Dreamsleave? The lesser Daedra have souls, so it would be possible that perhaps Meridia stuck a Daedroth's soul in Umaril's body. The Daedric Princes can choose whatever form they want, and thus have no genders and no way of procreating in the usual sense of the process. I'm sure they can, ah, have a 'good time' with created erm 'bits' as seems to have been the case with Hrormir and the 'Hag' Nocturnal in http://www.uesp.net/wiki/Lore:Song_of_Hrormir. Assuming the Hag is Nocturnal.
I could be wrong, though. :unsure: