I agree with Cami 100%. You can't guarantee that everything will go smoothly with a young puppy. Puppies bite (with a mouth full of needles), jump up (even toddlers are too tall to kiss from a standing position
), and have accidents (the sheer excitement of being in a new place and meeting new people is enough to make any pup "lose it" -- plus, being in an unfamiliar place will throw off his normal home routine). He might be making great progress in training and be exceptionally well-behaved for his age
but at 15 weeks old he is certainly not past those puppy behaviors, not nearly. Even under close supervision, accidents will still happen.
When Caney was about that age we took her to my grandparents' house for a family get-together, and Caney jumped up on my 3-yr-old niece, knocked her down and made her cry. I felt awful about it, but it wasn't a huge issue because everyone in my family owns dogs and knows how puppies are... it was just an accident.
From what you've described, it doesn't sound like your sis would be so forgiving
And also keep in mind that kids ages 1 and 3 are much more likely to cry after being nipped or knocked over than an older child would, or even a child of the same age who lives with dogs. If you wanted to have Kevin meet young children whose parents own dogs (especially big dogs) I doubt it would be such big deal.