Local authorities tested the bag - yellow Ziploc-styled - and the crystalline powder inside tested positive for methamphetamine.
The children had been trick-or-treating in the Keshena area on the Menominee Indian Reservation.
The tribe has set up sites where parents can dispose of their children's candy, WBAY reports.
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At this time investigators believe this is an isolated incident, however after police started to spread the word through the Menominee Nation after receiving a call from the parent last night around 3:00 a.m.
Trick-or-treating is a Halloween tradition, when children dress up in costumes and go from door to door and asking their neighbours for "treats". "Unfortunately zip-lock bags can open up, we don't know if there's more out there", Menominee Tribal Police detective Joshua Lawe said.
The incident has also forced Keshena Primary School to bar students from bringing Halloween candy to the school's events celebrating the holiday.