Diane Swanbrow writes for the University of Michigan:

The first national study of the prevalence of multiple partner fertility shows that 28 percent of all U.S. women with two or more children have children by more than one man.

... having children by different fathers was more common among minority women, with 59 percent of African American mothers, 35 percent of Hispanic mothers and 22 percent of white mothers with two or more children reporting multiple partner fertility. Women who were not living with a man when they gave birth and those with low income and less education were also more likely to have children by different men.

... "Raising children who have different fathers is a major factor in the intergenerational transmission of disadvantage," Dorius said. "Juggling all the different needs and demands of fathers in at least two households, four or more pairs of grandparents, and two or more children creates a huge set of chronic stressors that families have to deal with for decades." (Spero News)