My daughter still at 4 years old liked to "rub your soft arm". This means she would very gently caress the inside of your arm between the elbow and wrist. She even got to a point where she was scoping out arms and was excited about other peoples soft arm and not interested in anyone's arm who had fur on it, because it wasn't a soft arm. She only did this to those she was close enough to, so Dad, Mom, and big sis, but not her Aunt who she is next closest to. This drove the other two nuts and they would run from her, so I would let her if she was tired and needing comfort. Her Dad would come down stairs in a T shirt with a sweat shirt over his shoulders. She would ask if it was so she couldn't rub his soft arm and he would say, "Yep".
She seems to have grown out of it (now 5) and most often did this at cuddle time or when she was tired.
She nursed and then sucked her thumb...still a thumb sucker. I would rather the soft arm over the thumb sucking.