Before I let my pups go home to their new families, I let them interact with my adults (under close supervision). However, when I introduce them, I make sure that they are on the same level (on the carpet). It makes both less apt to feel as though they are inferior and that you are not introducing the new animal/pet as being "Alpha"....... (when you are carrrying it above/higher than the other animal). I know this may sound crazy but, it works (for me anyway). AND of course, I sit on the carpet with them so I am an arm length away at all times.
Jan