Yeah - this really reminded me of Ice Princess, and I agree. There’s something charmingly gentle and innocent about this sort of set-up. It’s as if the romance is almost secondary - they grow together and form bonds as people, and then that sort of morphs into romance.

And the younger siblings are central to all of that - not only do they provide a reason for the mains to spend time together - they generally pick up on the growing romance before the mains do, and then encourage it.