looking for Paula Green born about Feb 1940

I heard stories that my husband father might have had other children. 1940 census shows this to be true, he is listed as married to a Myme from South Dakota , they have a three month old daughter named Paula born in Wisconsin. Richard was a Truck driver for whole sale foods.
I am trying to find out how I would find what happen to Paula and her mother? Did they have other children?
How would I go about tracking them down? They lived on 15 St in Milwaukee at that time.
thanks for any help in this...