Better safe then sorry. But I would approach them & ask if there dog likes other dogs & let them smell eachother . Then from then on maybe they could say hi on their leashes. I have heard to many stories of little dogs being ripped apart right on the end of their leashes at the foot of their owners by bigger dogs. I like big dogs. But you dont take chances. Be friendly introduce them if its someone & there dog that you meet several times on a walk. Let them become friends. If the dog growls or anything forget it, maybe try again later. Let the big dog smell your hand & get a pet then introduce the dogs. Most likely the little one will have the additude
