Here’s a family-friendly, October 2025 roundup by city (plus the big Halloween picks). I kept it to confirmed, local listings with dates/hosts.

Belmont

Belmont Boo Bash @ Twin Pines Park — Wed Oct 29, 5:30–7:00pm. Costumes, games, treats; hosted by Belmont Parks & Rec. (San Mateo Daily Journal)
Trunk-or-Treat (Belmont Parks & Rec) — Wed Oct 30, 5:30–7:00pm (parking-lot event; decorated cars + candy). (San Mateo Daily Journal)

San Mateo

“Boos (and Brews) on B Street” & Trick-or-Treating (Downtown) — Sat Oct 25, 3:00–5:00pm; carnival games, crafts, music, photo ops, and merchant trick-or-treat. FREE. (City of San Mateo)
Día de los Muertos Celebration — Sat Oct 11, 12:00–3:00pm, Dr. MLK Jr. Park; altars, arts and culture, family activities. (City of San Mateo)
Hillsdale Shopping Center Halloween (Spooktacular / Selfie Booth) — Late Oct activations with kid trick-or-treat hour and themed photo booth fund-raiser. Check mall events page for exact day. (hillsdale.com)
CuriOdyssey @ Coyote Point — Ongoing family science experiences; check calendar for any October-themed specials. (CuriOdyssey)

Goblin Walk (Downtown Laurel St.) — Fri Oct 24, 4:00–5:30pm; costumed kids parade + treats from merchants. (cityofsancarlos.org)
Hiller Aviation Museum: Haunted Hangar — Oct 17–27, 10:00am–5:00pm; spooky aircraft displays and hands-on activities (very kid-friendly). (Hiller Aviation Museum)
Hiller “Pumpkin Drop” — Sat Oct 25; the museum’s signature STEM-meets-squash spectacle. (Hiller Aviation Museum)

Halloween Spooktacular (Red Morton Community Center) — Sat Oct 25, 12:00pm; ages 1–10, games and treats. (Active Kids)
Fox Theatre: “Deadwood Halloween” — Fri Oct 31, 7:30pm; theatrical Halloween night show (families with older kids). (Fox Theatre Redwood City)

Halloween Festival (Leo Ryan Park) — Sat Oct 25, 11:00am–2:00pm; games, entertainment, trick-or-treating (ages 2–12). (fostercity.org)

Downtown Burlingame Fall Fest — Sun Oct 26, 9:00am–6:00pm; rides, games, food, and costume contests—good all-ages option. (Burlingame)
Citywide Halloween Home-Decorating Contest — Register by Oct 19; judging Oct 20–22 (fun to tour with kids). (burlingame.org)

SF Chronicle’s 2025 Family Halloween Guide (covers additional kid events like Bay Area museum jams, pumpkin patches, etc.). Use it to fill any off-days. (San Francisco Chronicle)