Ariane and Sofia are not a few months apart in age. They are only
19 days apart in age; so it would be hard to claim that less than 3 weeks result in such differences between them - even though Ariane is indeed turning from a child into a young adolescent (something that was already evident at king's day) - but I agree with Kathia Sophia in some ways she still has something of a child in her (luckily; as she is only 12).
Alexia hasn't changed that much over the last months -
see for example this picture- I would say. So, also in her case I don't think the difference is due to their minor age difference.
I'd say the main issue at hand (and I think that's something we all agree on) is that everyone develops differently; and specifically in this age group (12-14) that results in very visible differences between girls. Clearly Alexia and Ariane are at a different stage in their development from child to adolescent. That's not better or worse; just different - but I don't think it's due to the limited age difference; unless Leonor suddenly looks all grown up at her birthday pictures in a few months. But even in that case she is 'later' than Alexia, as Alexia no longer looked a child in march 2018 (
see this picture).