The candy inside small, yellow "Peanut M&M" snack packs was replaced with some kind of pellets, which look like food for a small animal, possibly a rabbit.
"As soon as they opened it up they recognized it didnt look right and had a funny smell to it," said Lt. Jeffrey Wanger of Medford Twp. Police.
The suspicious candy was handed out to trick or treaters in the Hoot Owl, Tintern Mills and Taunton trace neighborhoods.
Police are warning parents to carefully check over leftover candy, especially those M&Ms, and report any that has been tampered with.
"Its very upsetting. Halloween is a family event, and we'd like to think we can trust our neighbors. Apparently we can't," said Sue Saccomanno of Medford.
The tampered M&Ms have been sent to the State Police lab for analysis to find out exactly what was put in the candy bags.
"I'm hoping it doesn't come up from a lab and say it was something dangerous," said Trish Emerle of Medford.
Police say they are going door to door in the neighbor hoods to track down whoever's responsible.
"Most likely someone trying to get attention, playing a practical joke," Lt. Wagner said.
So far, no one is known to have been made sick by this tampered candy.
Police say, when the person or people who did this are caught, they face charges of food tampering.
Anyone who finds or who has found candy that has evidence of tampering, or who has information regarding this investigation, should contact the Medford Police Department at 609-654-7511.
Persons with information may also call the Medford Police Citizen Tipline at 609-714-0302.
