Police say it was French mastiff and may have reacted angrily to the kids jumping on the trampoline. Hoquiam Police Sgt Jeff Salstrom was first on the scene and had to jump the fence where he saw the boy's head in the dog's mouth.
"The boy was covered in blood," said Salstrom. "I didn't know how severe his injuries were at the point, but I knew I had to get the dog off of him."
Salstrom said he first tased and then shot the dog as it still came at him.
"I heard three shots," said neighbor Robert Jimenez. "It was bang, bang, bang."
Saltstrom called out to Jimenez, desperate to get the boy, his younger sister and the baby sitter to safety. The dog was wounded and holed up behind a shed.
"It's scary, I tell you," said Jimenez. "It was a big dog. He must weigh 100 pounds."
The dog was cornered and held, and at the owner's request the dog was euthanized by a vet.
Salstrom knows all too well of the power of a dog. He just lost his K-9 partner, Enno, to cancer earlier this year.
"I love dogs," said Salstrom. "I was in a shooting in March where I got shot. I shot a bad guy who tried to kill me and another officer."
That suspect ended up dying in a fiery shootout with police the next morning. This is the first time Salstrom has spoken publicly about it.
"To be honest, I'd rather do that 100 times than have to deal with this," said Salstrom. "Not necessarily because of the dog. The dog was a danger. It needed to be stopped. But, because the little kids were injured."
Those kids were all treated for dog bites and released from the hospital. Police say the little boy needed several stitches, but is otherwise okay except that he's saddened that his own dog turned on him.