It's true! Some types of shirts come in multiple sleeve lengths (for example a short sleeve green tie dye and no sleeve green tie dye) but some types of shirts only come in one sleeve length (I think the baseball jersey is only long sleeve).
Well, I said short skirts, not mini. Mini skirts in this game would be bad. The short skirts literally make your outfit look like a dress. So the skirts, when paired up with a non matching shirt, make your characters outfit as long as a dress would be on your character.
And if anybody tried to turn that into a sexual meaning for a child's game, that's a bit creepy O.o
The bitter truth is better than the sweetest lie.
Even if they were mini skirts I don't think it'd be a problem. It's not like the characters strongly resemble real humans or that nintendo would add anything to the characters that would make short skirts inappropriate. I doubt even the most conservative parents would ever have a problem.
I'm very excited about all the new clothing options!