Need advice: Noticing an oral papilloma on a dog, don't know what to do next?

Extremely stressed out because we saw this flower-like growth in a pup's mouth AFTER they had been playing with our dog and two other daycare pups, which we think is an oral papilloma. It was bleeding in-between play, so that is how we noticed it. There is no way to know for sure until we speak with the parents, but I have no idea what to do about this situation. How would you handle it with the dog's parent? What about the other parents?

I'm so frustrated that this is happening because how do you not notice something like that in your dog's mouth? :(