West Highland White Terriers

Sparky likes to play with my son 7. The first time he had a kids party he liked the kids to pet him and play with him. Two months later when his friends comes over to play, he greets them and licks them and they pet him, then while my son and his friend are playing in his playroom, Sparky walks down the hall and barks and comes back to the living room. If they run up the hall to the living room, he runs to their feet barking. Sometimes if the friend walks from the living room without my son, he barks at them. I haven't seen him bite or even nip, but we are afraid he might.

He doesn't show any other agressive behavior.

No one since we got him (at 4 years) has harassed him or hit at him.

Thanks for any suggestions or thoughts.