I like to do handmade costumes but am not super crafty, so everything usually starts out as a hooded sweat shirt and sweat pants LOL
when my twin DD's were almost 2YO, they wore red sweatshirts and sweatpants with "Thing 1" and "Thing 2" labels (circles cut out of DH's old white t-shirts, lettered with sharpie marker!)
when they were 4 they wanted to be Murray and Anthony Wiggle so I got them the proper color t-shirts, made Wiggles logos out of paper and masking-tape looped them to the shirts, and paired the shirts with black leggings (and of course DH and I had to be Greg and Jeff to complete the group LOL)
A couple times DD1 has been a cat - black leggings, black hooded sweatshirt with felt ears sewn on the hood, face paint whiskers
DD2 has been a bee -same black hooded sweatshirt but with yellow felt stripes duct-taped to the torso, headband with antennae, and wings from a dress-up costume
This year I think one of them might combine black sweatpants and white hooded sweatshirt with a few embellishments to make a Panda costume, not sure about the other one.