BB pal Vann Hall found a terrific selection of odd halloween costumes for children, including this Little Trees car air freshener outfit. It appears to be a Little Trees-licensed product, yet they spelled "Freshener" incorrectly on the costume. Link
And if an air freshener costume isn't quite right for your baby, how about a Woopie (SIC) Cushion or Peeps peep, also available in adult sizes.
UPDATE: Greg from Daddy Types points out that that the trademarked name is indeed "Freshner."