I read she had a baby with her lover, but I thought she has no physical form. So how did she have a child?
Maybe she straight up crafted one in the likeness of her lover rather than physically had one? It’s certainly less disturbing than the typical rapey exploits of other gods looks at 99% of classical mythology.
It likely was a more metaphysical thing than resllu mateing
That would only really be necessary if her partner was the carrier of the child. There’s no need for her to really get intimate with her partner when she could just have her children fall from the sky inside a chunk of moon rock.
They’re deities. Mortal logic doesn’t apply.
Iirc Malorne jumped in the sky and Elune saw him from above. She liked the attractive deer and inserted some of her moonlight stuff in him and made him pregnant because she can’t give birth by herself probably.
Ehhhh I feel like the “created in his likeness” thing is more likely than her knocking him up. She’d need to change his whole biology for that to even make sense.
Don’t try to find sense in it, it’s a world full of magic 
Remember that time Athena sprang, fully grown, from the forehead of her father, Zeus? Literally anything can happen with deities, until (if) Blizzard decides to expound upon it.
Just use your imagination. Or the internet, if you’re imagination is… lacking.
I dont say this is a canon fact or true, but just a tin foil hat theory:
Elune may be a massive sentient space station. Sort of like Graymalkin/Professor/Ship from X-Men.
Perhaps a Noah’s ark of destroyed planets. Containing a vast variety of creatures or just their DNA.
So when she “birthed” a child with Malorne to produce Cenarius, that could be the result of a DNA lab within this “Sentient Ship”.
Her “tear” could be a form of radioactive liquid produced from the exhaust. Like some cars produce water out of their exhaust.
Just a possibility.
There’s a lot of artwork from the RPG of Elune in the form of a Night Elf. It would make sense if, like Sargeras, Elune has an avatar. Perhaps more than one.
Her name is Tyrande Whisperwind.
Well, given that Cenarius is depicted with a deer with Night Elf resembling upper half its possible that Elune could have used one of the earliest high priestess of Elune as a vessel for her power, similar to the Night Warrior thing.
According to legend she does have a physical form she can take. As a true deity taking physical form and having a child is well within her ability.
I mean hell she made stars just to honor her beloved friend Ysera. That is an act of great power far beyond just taking physical form.
It’s also worth noting that to the tauren, Elune (Mu’sha) is just the moon, and doesn’t take the form of an elf or anything.
So people can get their heads out of the gutter with that whole deer on elf nonsen-- Hey! Stop it! Stop thinking about it!
Of course Elune has a physical form. Otherwise, it’d be too challenging to fit her in a future raid.
Christians don’t seem to have a problem with their formless deity siring a child.
You’re making a lot of assumptions about God the Father’s erm… cup size.
Zeus impregnated a woman by literally raining down on her.
Her name is Tyrande Whisperwind.
“Say my name”
“Tyrande Whisperwind, Elunes avatar of vengeance”
“You’re god damn right.”