Okay some cute outfits for a 12 years old is probably be Aeropostale! They are really cheap and outgoing! They are almost like A&B/Hollister but they are way cheaper and all the clothes are very comfy! And I would suggest that you wear for Summer: Cute Aero tee w/ dark wash skinny jeans and maybe some converses!
For Winter wear:
A cute tee with a jacket/hoodie over it with some skinny or flare jeans!Maybe add a cute headband over it to really bring out ur style! And any other accessory will work! For the not so warm not so cold days wear:
A pair of converse with a Henley not buttoned and a matching Cami inside w/ skinny jeans! (they will rock out your look any day!
And for really stylish looks wear:
A cami w/ a shrug and some black skinny jeans or straight leg, w/ some flats!
For really hot summer days wear:
A cute tee w/ a cute skirt/shorts and flip flops!

Hope this helps and I am a 12 years old as well so this will be good advice!