Katarina

Katarina (from League of Legends) by Tanita Osaki
Photographed by Witchsister Photography

Sarah Kerrigan

Sarah Kerrigan (from StarCraft II) by Freia D.N.A. Raven

Photographed by Andrey Shinkarchuk

Merida

Merida (from Disney's Brave) by Tina Rybakova
Photographed by Dasha Kond

Kids: Frodo

Baby Hobbit (from The Lord of the Rings)

Source: Imgur via Reddit

Kids: Claptrap

Claptrap (from Borderlands 2)

Photographed by Dangadelha at PAX Australia

Rikku

Rikku (from Final Fantasy X-2) by RyuuLavitz

Kids: Pit

Pit (from Kid Icarus) by Keaden

Photographed at AWA 2013

This is one of the most ridiculously adorable boy's costumes I've ever seen.  I seriously doubt that he's ever played the game his character is from, though.