Tiny Tux

If you are looking for a small size Tux outfit, I can from experience recommend http://www.tinytux.com/ .  This company has dozens of styles and color combinations.  Complete sets, including shirts.  From size 6mo all the way up to Boy's size 20.  Reasonably priced with very prompt service.  The figure here is a 38" figure and is wearing size 3T. 

My thanks to Canon John Jordan for alerting me to this source for children size tuxes.