Here's a fun idea: if you're writing a book where the protagonists are children, maybe consider not having them marry each other later in life.
Image: Warner Brothers
This is a trope that is nigh ubiquitous in YA novels and it's creepy as hell. The reason it exists at all is that, forever in our culture, happy endings have been tied to getting married and having kids. So when the book is over and the teenage protagonist is an adult, to show that the ending is actually happy, everyone has to get married. And since it's not interesting to have your hero hook up with a rando that no one's ever seen before or cared about, it's gonna have to be one of the other characters that's been around forever, who are invariably their childhood friends.
I get all the structural reasons for this. But consider this argument: it's really weird. What percentage of the population marries their childhood sweetheart these days? And, thanks to the story we've just read, the characters pairing up made their first impression in the reader's mind as a child. Kids are marrying kids. Why.
Here's another reason it's weird: this trope is almost always paired with the protagonist having dated no one else, or, at least, having dated anyone else in a serious manner. That's even weirder.
Not because it's harmful to pass along the idea that everyone's first real love is their only love, but because it doesn't feel realistic. The first person you date is really unlikely to be the person you marry these days. Even the second person you date isn't going to be that person. For the reason that a) young people don't have a great barometer for what makes a good spouse b) they're going to change as they age and want something different. Think back to the most important quality of your dream person in childhood. Is it the same as it is now?
And it almost always turns friends into loved ones, as if love is some kind leveled-up friendship. "You have been friends for three books. Now you have unlocked Romantic Relationship." Or, even worse, it comes off like the cheat it is and like the author has paired the only boy and girl with actual character development and history together. (It's always a boy and a girl. It's very heteronormative and plays hard into the idea that single people of the opposite sex cannot be friends.)
Everyone had a giant fight about who should have ended up with whom when the Harry Potter books ended, but how about Harry, Ron, and Hermione ending up with people they hadn't met as prepubescents? Harry not ending up with Hermione was the least tropey thing in the Harry Potter books and I was so happy about it he could have married a table and I would have done a dance.
I love Diane Duane's Young Wizards series and I think the relationship between Nita and Kit has developed in a much more natural way than is usual in this trope. I even found myself liking it a lot in the last book. Would I be happier if they had just stayed friends and had friend drama instead? Yes. Because even as well as Duane has done it, this trope is so ubiquitous that it feels like a requirement more than an authentic story beat.
Let's reduce this trope's prevalence to how often it happens in real life. Or at least closer to a generous 10% of the time.