The one page, typed letter was slipped under Brenda Milson's door on Friday.
Her grandson, Maxwell, stays with her in the mornings during the summer. The letter complains about the "wailing" noises he makes while playing outside.
The author of the letter said that the family should go live in a trailer in the woods with their wild animal kid, or have him euthanized.
James Begley, Maxwell's father, reacted to the letter saying, "Whoever wrote it is a disgusting human being."
Brenda Millson, the boy's grandmother, said, "By the time I got near the end of it, it got so bad, I was shaking, and I was shaking and crying at the same time."
Canadian police are investigating.
Meanwhile, other neighbors have come forward to show their support for Maxwell. One neighbor even left a letter of support, with a new ball as a gift.