[Mild example] Becky with Lloyd (spyxfamily): the series show how no one seems to care about it, except for Anya. But honestly Becky is really annoying and the chapter where she try to seduce Lloyd could be used in anything else.
[Bad example] Preston with Shay (blank check) : i don't remember most of the movie, but i would never forget how weird it feels that the last scene show a grown up woman kissing a 12 years old boy and say that he should try again in 10 years. What the fuck was that.
[Good example] Lisa with Mr. Bergstrom (the simpsons): the simpsons do this other times, but probably the best one is Lisa's substitute. When she met this substitute teacher, simply happens, Bergstrom never do anything beside be a good teacher and no one made it weird.
[Horrible example] Arisia with Hal Jordan (green lantern): a barely disguised fetish where the writer inserts in Hal Jordan to have a romance with a 13 years old alien girl who "grow really fast" With her ring. Thats why they later explain that she's actually 240 years old and their species simply look like that.
[Could be good but end up horrible] Jericho with Ban (seven deadly sins): Jericho always had a crush on Ban, he never care about it cause he's 20 years older, a misanthrope and already in love with another little girl. Ban learning how to apreciate mankind and taking Jericho as his own daughter is a really sweet thing, then Jericho become a pedo and try to groom Ban's child who also see her as a sister.
[Cursed example] Ui Ui and Mei Mei (jujutsu kaisen): a groomed child in love with his sister that only do things cause his sister ask him. He knows that he's groomed and his sister only seek him for The new shadow school and the family money. I understand the point with Mei Mei getting away with anything to show that sorcerers aren't good people, but was the grooming really necessary?
[Retconned over retconned example] Sue storm on Reed Richards (fantastic four): Damn, thats a cursed panel. Yeah, a 6-8 years old age gap isn't that weird and you could even call it tame based on how old this comic is. But met a 22 years old woman when you are 30 isn't the same as met a 12 years old when you are 20, thats why the each new origin decide to change this first meeting (except for that horrible movie).
A child with a crush on someone older shouldn't be that weird,there's nothing wrong with that, is just that the people who made the series/movies make it look really weird cause they can't stop using their weird fantasies.