I have a 12 lb cavalier king charles spaniel with my baby girl and they are the best of friends. Most important, my Cav, Louis is SO patient with Ella. She will try and steal his toys and he wags his tail. She will wait until he is asleep and then growl and grab his ears and shake them like chew toys and he wakes up and wags his tail and rolls over and lets her wrestle with him. He almost always lets her 'win.'
Its the personality of the 2nd dog that matters. You want a patient, happy dog who is well socialized. I have to say, Cavaliers are just an exceptionally easy going breed. I belong to a meetup group and they are all super silly and relaxed and even when they play, it never seems to escalate beyond a few warning growls. Great breed (not as great as Yorkies...
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