Two short guys each with a bloodthirsty streak, I think at one point they worked for the Monarch. In one episode Brock asked them to 'put some fear in someone' but 'nothing lethal', then decides he shouldn't be working with the two at all.
Swiped from Wikipedia's List of The Venture Bros. characters article:
Tim-Tom and Kevin (voiced by Christopher McCulloch and Doc Hammer, respectively): Achondroplastic dwarves who were Dr. Girlfriend's Murderous Moppets in her solo career as Lady Au Pair.