Anglebow- I just saw this.. Please do not blame the older dog. I am afraid this is a problem that could have occured easily. Adult dogs do not see puppies as dogs, just like dogs may not see an infant as a person either.
I am sorry the puppy got hurt. I never let any adult dog around my pups except the mother- then the father if watched VERY CAREFULLY.. Even then- that is a streatch.. I was lucky - I had another female I could get around the pups that was reliable- but still never left unattended.. Do not blame yourself.
Keep that dog away from the pups- or any dog- including dogs from the outside of your home. Raising pups is hard- its a constant roulette of moving this dog there and that dog here.. so to speak..
I hope the pup goes to the vet as infection in a young dog can happen real fast, and a puncture can easily get infected.