Talec said: if you ask me, they suddendly became much bigger ~
Go check, they were always that big. They're the same size as her twin sister's. Kyou stands with her chest forward and shoulders back, making hers look bigger, while Ryou stands with her shoulders scrunched, making hers appear smaller. It's a masterfully created illusion by KyoAni.
hmm, imo clever chap. Anyway, for me it makes here more adorable then Kyou, it's a waste that her Arc/Personality in Clannad (and AS) were so boring. ~