Really important that if a dog gets hold of your child, do not pull or let others pull the dog as it can make the injuries worse, if not fatal. Have someone lift the attacking dog by up their back legs, this is where all their pulling power is and reduces the damage they can cause, then try to prize open their mouth with a stick / pole or whatever you can find.
If this fails - You can try to hit them in the balls if they have them / kick them or punch them in the side of their abdomen / strangle them until they pass out / hit them over the head with a rock or heavy item to make them pass out. These are all horrific things to do, especially if you are an animal lover, but your child could die.
Some dogs will respond to food and let go, so if you have food on you, that’s worth a try. Also, as hard as it may be, last ditch attempt could be to try stroking the dog in a sweet voice as it might confuse them and make them see you as not a threat and release their grip.
Dog attacks are terrifying. Having some things to try can really save lives.