ooo thank you this is a really interesting question! when i write childe in canonverse i'm usually writing him as gay- this ties in with a few other headcanons i have about him spending his adolescence as a fatui soldier, and the type of sexual awakening he likely had in that environment, but i think he definitely also carries some delicious religious guilt about his sexuality that caused him to try a few times to straighten himself out (see my previous answer about him and skirk, signora, the tsaritsa...hehe). i feel like his obsession with constantly talking about, and projecting an image of, his perfect family is also really interesting if you view it in that context...and like, not to get too meta about it, but you wouldn't have to stretch (heh) too far to see the metaphor in childe falling into a gaping hole as a child and coming out different.

bennett i tend to write as much more freewheeling in both canon and AU, like, i really don't think he thinks about this kind of stuff at all. i think he could be attracted to any type of person, and down to try having any kind of sex. i think he just fundamentally does not understand childe's various neuroses around this topic at all LOL...for how lacking this half of the answer is i will throw in a depressing hc for free: i think he prefers to bottom because if his luck causes anything to go wrong, then he'll be the one bearing the brunt of the pain instead of his partner

in my head they're quite opposite when it comes to cleanliness, like, my hc is that the combination of childe's military upbringing and the monster he's hiding inside his own body results in him being extremely preoccupied with looking as normal as possible, and so he's almost always groomed to an obsessive extent; and bennett's a grimy little urchin raised in a house full of stinky half-feral old wilderness men. and i think that occasionally drives childe fucking crazy in the exasperated way you feel when your dog rolls in a pile of shit, but also in a fond older-brotherly (waggles eyebrows suggestively) way like he's constantly licking his thumb and wiping dirt off bennett's cheek or kneeling to hike up his socks and tie his shoes. and then he jacks off about it. FREAK

HAHA ok walk with me again into my mind palace.....i think bennett has no blowjob technique whatsoever BUT he makes up for it with a) a nonexistent gag reflex (from regularly accidentally giving himself food poisoning on his adventurer outings!) and b) insane, off the charts levels of enthusiasm. like, nobody ever tells him that he does a good job at anything...so he'd happily slonk your shit twice a day for the rest of your life if you told him how much you loved the way he did it. (even if there's teeth sometimes.) for sucking childe's cock specifically, i think bennett's always secretly a little concerned that making childe cry every time he blows him is actually because he's godawful at this and childe's just being nice by not saying anything—despite childe's loud, embarrassed protesting that it's not that, and he is NOT crying, shut up!!!—and also i think sometimes he pretends to gag on it to feed childe's ego.

walk with me...we have to consider that taru honed his craft on some of the most insane pussy in the galaxy. skirk's? full of teeth and tentacles. signora probably tried to crush his skull with her thighs the whole time he was trying. the tsaritsa? i think this is the only time he ever came close to pleasing anyone, but it's entirely because it was during that brief moment where he was her newest toy and she was obsessed with how fresh he was, how shiny. and he can't even begin to explain what she has going on down there. biblically accurate angel pussy. his tongue stuck to it like a frozen lamp post

so i think he's kind of shocked at himself when he makes bennett come in no time at all. he's used to this being a power play, a way to remind him of his place and humiliate him until the receiver gets bored, but bennett's all teary and glowing and looking down at taru wide-eyed like he's some kind of sex god. and it took so little time and effort that he didn't even have a chance to use his foul legacy tongue...

i honestly, honestly believe that this is the beginning of the end for taru sanity-wise. like, bennett's bad luck has to cause something to go catastrophically awry during it: maybe he gets a nosebleed, maybe he accidentally busts taru's lip, i justttt think there's going to be blood drawn during it somehow. and bennett rears back with pinkish saliva stringing between their mouths fully expecting taru to be horrified and disgusted but instead his face is flushed bright red all the way to his ears, and his weird dark eyes have gotten even darker and weirder, kind of like when you catch the glint of an unseen animal's eyes in the shadowed spaces between the trees deep in the woods, unsettling. but taru just smiles at him and takes bennett's face in his hands, kisses him again, gentler this time. and the strange moment passes, but neither of them forget it.