Referring to a group of trick-or-treaters as goblins may not be as far off the mark as calling them ghouls. Goblins are small, grotesque, evil or mischievous creatures or spirits that seek to harass and annoy. At least during Halloween celebrations from earlier centuries this may have been a very apt description when there was more emphasis placed on the "trick" portion of trick-or-treat.
Goblins often, when not trick-or-treating on Halloween night, wander the countryside looking for a good place to call home. This could be a grotto, a cave, or best of all, your home! In French folklore goblins were especially attracted to homes with beautiful children and plentiful wine. With the burgeoning affluence of the bourgeois here in the San Francisco Bay Area there are plenty of homes sure to make a goblin happy. Upon taking up residence, goblins seek to annoy its housemates with minor acts of mischief. Banging on walls, slamming doors, rearranging your furniture, removing your covers when you are asleep, and resetting your alarm are all signs of goblin activity.
Not all goblins are necessarily bad. In some cultures the prefix "hob" means good so that a hobgoblin referrers to a good goblin. In those cultures hobgoblins are sometimes thought to, when in a good mood, help the household residents by doing chores while they sleep or even going so far as to help with the parenting by disciplining bad children and delivering gifts or good fortune to the good. However, in the American tradition all goblins are evil regardless of the hob prefix.
You may be interested to know that goblins are part of a much larger but very interrelated group of creatures and spirits which, in addition to goblins and hobgoblins, include: bugbears, bugaboos, bogeys, bogys, bogies, boggarts, bogle, boggelmann, bock, bogey-beasts, bug, boo, puca, bogeyman, and boogieman and all refer to the same or very similar type of creature or spirit.
In the British Isles, the Welsh preferred the term bugbear or bug. Bug meaning ghost in Welsh. Scots call them bogles and the Celts referred to them as bugaboos or boos. In England they often went by bogey (or bogy, bogie). By the way, this is where the military picked up its bogie designation for unidentified objects. Bogeys travel alone or in groups causing mischief but while a generic goblin can have many forms bogeys are usually large and black, are active at night or in very dark places, and are very fond of scaring children. A very famous type of bogey is the bogeyman or boogieman. In Germany it is called the boggelmann. While they all refer to the same thing, a bogey, they are usually called a bogeyman when they are traveling solitary. In generations past, parents pretended to be able to call bogeymen at will in an effort to scare their children into good behavior.
A particularly nasty type of bogey is a boggart. These usually inhabit a specific location like a home, graveyard, cave, or field but can take up residence in the body of an animal or even a person. Unlike their goblin and bogey relatives they do not have a physical form. Their activities are poltergeist in nature causing mischief by moving objects and scaring people with horrible noises and maniacal laughter. They've been known to hit, scratch, and pinch people and in some cases carry them away. Interestingly, they are thought to be scared of cars and therefore relatively rare today.
So now you know. It's now up to you to decide if referring to your trick-or-treaters as cannibalistic flesh eating monsters or small grotesque evil creatures is appropriate.
I've already made up my mind, it's Halloween, of course it is appropriate!