In fact non social species, like felines, are unmoved or even aggressive toward babies not kin related to them.
But we are primates, and being primates very social, we are subject to trivers reciprocal altruism, in other words: childs are very prone to help strangers if they feeds them. They can be adopted and parassitated as muscular force in exchange of a small piece of the meal, smaller than those of the natural childs of course, as foster care studies have demonstrated. So we can find others child very attractive too, because they can be very useful to us, because they are easily exploited due to the long period of dependence from adults.
This is not directly related to the cutness, anyway, that is a physical trait, with specific characteristics (big facial elements, head bigger than the body, small arms, etc.). If one puppy develops those traits to deceive his parents, those traits will be there to be seen by all the other people too. Unless there is a specific adaptation to resist such aestetic feedback in non kin related puppies, like in some non-social species, the brain response at a cute face is the same.
I find the bunny cuter than any human baby I ever seen, and I believe that the majority of people will share the same feeling, but our opinions are aneddotical and do not constitute scientific proof. What we need is to take a statistically unbiased sample of people and asking who is cuter between the two, eliminating in this way the random influences (positive or negative) on the istinctive cuteness reaction caused by cultural bias or personal experiences, because those should be distributed equally and then cancelling each other, while the genetic bias should emerge as the dominant result being shared by all the people in the sample. Maybe someone will do a study about cuteness in the future, corroborating my theory or falsifing it. But the point is that there is nothing “unscientific” about evolutionary psychology. It’s a science, and it’s the best model of the human psychology ever developed.