My younger daughter recently inherited her older sister’s supergirl costume and LOVES it.
My 7 year old daughter, Sakura, wanted to go to the convention as Ahsoka Tano from Star Wars: the clone wars. We’ve put a lot of work into her costume.
Everything was custom build. Her backpack with Rotta in it was made with a simple carboard box and Fimo for the creature. Her lightsaber was made from wood and plastic and lots of paint. The headgear took longest to build. It was created using a wireframe covered in the lightest Fimo you could find. The costume was done by mommy and grandma. Make-up was applied later on.
Special effects added for dramatic effect, of course. :-)
My 2 year old and 4 year old daughters meeting R2D2, dressed as Finn and Chell (from Portal). They were so excited.