Universal Orlando's Halloween Horror Nights is now the world's largest theme park Halloween event, in terms of attendance and income, drawing fans to Universal Studios Florida throughout late September and October.
Some parks offer kid-friendly Halloween events, including (predictably) Disney, which hosts Mickey's Halloween Parties at Disneyland and Walt Disney World. At these parties, the focus is on unlimited trick-or-treating, not scares and haunts. They provide one of the few opportunities for grown-up fans to attend Disney theme parks in costume.
Walt Disney World
Tokyo Disney Resort