MK is decorated for halloween so you still see that even though you are not doing the party.
Seaworld has a spooktacular event with trick or treating on weekends in October - is included in normal admission price - we are going this year for the first time.
Not sure re busch/universal.
Also DTD is decorated for halloween and has tick or treating on actual halloween.
Universal studios is decorated for halloween horror nights
Seaworld was my fave out of all the parks decorated for halloween and the spooktacular event is great gave loads of candy too here is some photos of seaworld sorry they are not great but will give you a little idea
Some of the pumpkins
This is part of a fun maze
My brother in the bubbles he's going under the sea lol
Seaworld's event is well worth visiting - it's included in regular admission and they have many "original" characters out and about (mermaids, sea-witches, jelly fish on stilts etc)
There's usually a Sesame Street themed area and lots of trick or treat goodies to be had.
As you want it to be kid friendly and not scary then you are definately best avoiding Universal's Halloween Horror Nights. It is great for teens and adults (us included) but not for small children or those easily scared as some adults find it to frightening. We love it