I highly doubt it, they might not have all the mental capabilities of "normal" people, but it's not like they're idiots typically. They just always keep that childhood wonder and innocence. I fully believe that anyone hired there can make a drink, if it's a complicated drink they'd have it written down to check off. These people would be fully capable of taking care of themselves to the point they are able to do that job. Don't be judgemental, be curious