Please, it is your duty to help by reporting the location of this dog.
If there is proof of rabies vaccination, it might save the child from the painful round of shots. You may also be saving the life of another child by having this dog picked up. Just because the owner has control of the dog now, does not mean it could not break free from the yard and attack you or a grand child.
Dogs have a "pack" behavior which means if all three dogs were loose together, it only takes one to start the agression and the others will follow. Might even take down their owner some day.