An older male baby sitter

Back in the 1950s sex wasn’t on my mind at all since I was only about 9 years old.
My mother and her girl friend were going shopping together. So we drove over to her place and mom left us to be baby sat by this womans husband.
We were supposed to be going swimming later so my sister and me had on our bathing suits.
We heard mom and her friend pull away in the car as we sat watching tv under the watchful eye of our unknown sitter.
He was an average build not big at all but older, about in his 40s.
We sat there watching tv together. I would look over once in a while to catch the man rubbing his crotch area and staring at us.
Finally the man came over to the sofa and sat down beside me. I almost felt naked sitting there in my bathing suite. I was small with a slender build at that time. I sat there trying to watch tv but I couldn’t help peeking beside me to see him still rubbing his crotch area.
My sister was almost asleep at the other end of the sofa. He noticed this and said he would place her in the bedroom for a nap. Then he returned and sat down right beside me so that I could see him. His pants were undone at the top and his zipper was down.
He reached into his pants and was rubbing what ever was in there.