I read this in that if you look at their personalities why do they hang out at all?

They only one I would question is Hermione.

But they kind of grew in to liking eachother you know.

Harry talked to Ron on the train and Ron seemed to think Harry was cool and friendly enough. Perhaps Ron liked being in the know about magic more than Harry. Or was just eager to have anyone talk to him. Harry also stuck up for Ron to Draco so that probably impressed him (hopefully thats not just movie canon I need to reread, my mind is perverted by those films). Harry also was probably eager to make any friends. He had never really had any and Ron was nice and seemed to like him/think he was cool. Harry and Rons friendship I get. It started young and I think it was a give and take of Ron showing things to Harry and Ron thinking Harry was impressive in demeanor and fame. Also they both can make jokes and be funny.

They didn't get along with Hermione until the troll incident when they were impressed she took the heat off Harry and Ron by taking the blame for letting the troll in. They thought she was a total snob cuckoo nerd until she did something nice/cool for them. Ron was probably more judgey than Harry, but I think Harry too found her snobbish.

But besides that I dunno for them really, maybe its just they started getting into trouble together and hanging out and being around each other (since theyre all Gryffindor, so same schedules) they just kind of grew on each other.

But I still don't really think they'd be friends with Hermione. She doesn't seem to have many similar interests or personality traits. Maybe she just offered them help a lot since she was desperate for friends (since it seemed no one liked her) and to seem cool and get recognition from helping with her knowledge/skill, and they liked having someone who wanted/could help them out a lot whether it be with homework or their late night misadventures. I think of her as their mom in a way haha.

I definitely think early childhood friends are more based on convenience than anything. Children don't have super distinct personalities and don't seem to make conscious decisions about who and why they make friends with someone.