"I know they’re little kids and Ouji is definitely a pretty realistic kid, but I hope it doesn’t take a crazy long time for him to notice Himeno T-T"
Well, to be fair, I don't and can't expect much from a not-even-junior-school kid. They did not know anything about love with opposite sex. All they cared were games, cartoons, and sweet things. In fact, in some schools that I've known of, you'd get 'bullied' for showing any affection toward opposite sex for liking him/her.