It's only felony conspiracy if they conspired to commit a felony, which petit larceny is not.
If, however, they made it a robbery (which would be difficult in NYS) then you might be able to charge conspiracy as a felony.
I'm assuming the value of all things stolen was under $1000, by the way.
First google definition: Robbery is the crime of taking or attempting to take something of value by force or threat of force and/or by putting the victim in fear. ...
Second google definition: Law . the felonious taking of the property of another from his or her person or in his or her immediate presence, against his or her will, by violence or intimidation.
Shoplifter definition: a person who steals goods from the shelves or displays of a retail store while posing as a customer.
Sure does sounds like they committed robbery. Shoplifting requires stealth / deception.
Your mileage may vary of course.