yeah you cant exactly expect an elementary student to unlearn homophobia right off the bat. in general, i hope the relationship between fumi and shun will become more brotherly.
I think they explained it like Mio and Shun would explain it no? It's hard to give perfect and profound explanations in real life, and I think the manga did a good job with that and portraying how the characters themselves would handle it. I like that it's giving Fumi a chance to figure things out a bit himself too, like how when he tells Mio he doesn't like being different because people will call them weird, and then realizes HE'D just done the same thing and rushes to apologize to his brother. It was mature for a seven year old and at that age there's only so much they can explain and make him think about that he will actually grasp, it'll be much more impactful if he comes to these realizations himself.
I know he wanted his little brother to understand and hear them out but I honestly feel like they could have handled that better. I mean he only thought it was strange because that is what he's been told his whole life you know. Hopefully in the future its a proper scene between the brothers in the future^^