The Arts Council of Princeton hosts a Tricks and Treats activities and games (normally at the Princeton Shopping Center, mid October).
When I last volunteered, the Princeton Graduate Molecular Biology Outreach Program was on hand, enabling visitors who wanted to investigate the orange color of pumpkins. They were gearing up for, or otherwise promoting the Annual El Dia de los Muertos – Day of the Dead – event in early November. Click on the link to get more information and get it on your calendar. I helped Melissa, of the Arts Council of Princeton set up but had to leave before the Alex & the Kaleidoscope sing-along, Sweetberry Bowls tastings and parade. Costumes were encouraged but not required which meant everyone could join in! If I could, I would have had dinner at Nomad Pizza or The Pho Spot in the Princeton Shopping Center.
Many of the events at the Arts Council of Princeton are free and open to the public.