The Hello Halloween Pumpkin Parade, an annual Halloween parade in which approximately 1,000 children under twelve dress up to form a parade that spans the 700m long zelkova-tree-lined section of Omotesando, takes place for the 28th time this year. Plus, in addition to the parade itself, there will also be a special Okashi Rally Map available that shows the whereabouts of a number of participating shops in the Omotesando/Harajuku that will be giving away free okashi (sweets) to children.
Venue: around Harajuku/Omotesando area
How to participate: children (under 12 years-old) who dress up in costumes can join the free-contents To join this event, you have to be under 12 years-old, but, you can watch the parade and see a lot of cute costumes for Halloween! So, adults can also enjoy this event! Official website here
I also found some sort of brochure with more details on other events. The brochure is in English and you can download it directly through here
Flavors of Japan 