To shorten means to make friable or crumbly, as when making bread or pastry by rubbing butter, lard or other fat into flour (short pastry is an example of the use).
Shortening is the fat that is added to the mix, but here I think baby is actually helping to make bread
Shortnin' bread - a term used to describe the preparation of many Southern American quick breads.. like corn bread with strips of bacon. The word "shortening" actually refers to all types of fat used in baking, including: butter, lard, solid shortening, oil and margarine.