How could the old evangelist tell which homes had babies?
The old evangelist could tell which homes had babies by looking for diapers hanging on clotheslines. As he came into a city by train, he noted that clotheslines with diapers indicated an infant lived there, since there were no washers and dryers in those days.
Les explains that the evangelist traveled only by train in those days. As he would come into a city on his train, he could always tell which homes had little babies in them. The indicator was diapers hanging on the clothesline. There were no washers and dryers then, so a clothesline with diapers meant that in that home there was an infant, a baby. Les uses this to illustrate that the spiritual life is a parallel with the physical: believers begin as babes in Christ and will have failures, just as infants are not trained to go to the bathroom.