Applescript date conversion
If your example is in the order year, day, month and you want MM/DD/YYYY then this code does the job

set creationDate to "2013-04-03"
set [Y, ordinal, M] to the words of creationDate
set the text item delimiters to "/"
set date_string to {M, ordinal, Y} as text


What you are attempting to do with the date command is unclear.