From Legal Momentum:
Over one quarter of U.S. children under age 18 reside with only one of their parents, and as many as half of U.S. children may reside in a single parent family at some point in their childhood. The vast majority – over 85% – of single parents are single mothers.
Poverty is widespread and severe in single mother families. According to the recently released Census Bureau data on poverty in 2010, people in single mother families had a poverty rate of 42.2% and an extreme poverty rate of 21.6%.
Some call it a bug.