Some dogs just really seem to hate puppies. I've heard many people say this about their dogs, and I've experienced it with one of my own dogs (He doesn't instantly attack them, he just has a lower tolerence for puppy antics).
Most responsible thing to do is leash the misbehaving pooch. My dog that has low tolerence for puppies also HATES boxers and english bulldogs. I had to start looking way ahead to see if there were either of those breeds coming and leash my dog if there was. Now, after quite a bit of corrective training, I can leave my dog offleash around those 2 breeds and feel confident that he will ignore them.
My tactic for training my dog is just as I said. We went to the dog park, he was allowed offleash until I could see one of his hated breeds coming. He was then leashed. If he approached them too hastily or I could see him tensing and preparing to attack he was corrected. I used a pinch collar on him because I found it much more effective. Every dog is different though, and while I use a pinch on my one dog I would never use it on my other (He's a very sensitive fellow and only needs vocal or light corrective actions). If you decide to use a training aid like a pinch or choke collar PLEASE learn to use it PROPERLY. So many people are unaware that there is a right way and numerous wrong ways!
It will take patience and determination. If your friend isn't willing to put in the amount of work that this will require then I would agree with BenMax 100%. Don't take the dogs to an off leash anymore.
"He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion."