The passage describes a 'quiet crisis' affecting American infants and toddlers, covering infant mortality, low birth-weight babies, immunization, poverty, and foster care. Among the four given options, only 'Low birth-weight babies' relates to the cluster of issues affecting vulnerable young children discussed in the passage. The other options (orphans, working mothers, foreign policy) are either peripheral or absent.
Note: None of the options precisely captures the passage's true focus on infants and toddlers in crisis; we have picked the option most directly linked to the discussion.