Originally posted on Gaming.SE for a similar question.
Mixed-race children like Jagar Tharn exist, but are exceedingly rare
The prototypical example of a mixed-race individual is Jagar Tharn, villain of the first game: Arena.
While there was a lot of in-universe debate over what he was, it was clear that he was an Elf mix, but didn't have human lineage (i.e. Imperial, Nord, Breton, or Redguard).
"I just don't trust that mongrel Elf. Part Dark Elf [Dunmer], part High Elf [Altmer], and part the gods only know what. All the worst qualities of all his combined bloods, I'll warrant." He snorted. "No one knows much about him. Claims he was born in southern Valenwood, of a Wood Elven [Bosmer] mother. […] Human blood seems to be the one missing component in Tharn's ancestry."
–The Real Barenziah, Vol 4
The Imperial Library article on Jagar Tharn also weighs in:
He is said to be part Bosmer and part Dunmer.
I think this assessment is plausible, given that he has the skin tone of a Bosmer, but the eyes and height of a Dunmer.
To my knowledge, there are no other mixed-race individuals in the games.
Among species that can interbreed, children normally are the same race as their mother
The in-game book Notes on Racial Phylogeny states the following:
- Elves and humans can mate and produce fertile offspring
- Offspring of such unions match the race of the mother, but "traces of the father's race may also be present"
- Argonians and Khajiit are believed to be infertile with humans and elves
- Insufficient evidence exists to determine if Orcs are infertile with humans or elves
Regarding Orcs, Oblivion has a sidequest involving Agronak gro-Malog discovering that he is the son of a vampiric Imperial. So interbreeding between Orcs and Humans, even vampiric ones, must be possible.
Note that this report, especially with phrases like "traces of the father's race" does not match Jagar Tharn's situation, lending further evidence to mixed-race children being very atypical.