Final answer:
An 18-month-old child in multiple foster homes likely has unmet safety needs according to Maslow's hierarchy, as the child's vigilant behavior suggests a lack of personal security and stability.
Step-by-step explanation:
An 18-month-old child who has been in multiple foster homes and vigilantly watches everyone may be displaying signs of not having their safety needs met, according to Maslow's hierarchy of needs. This level of needs encompasses personal security, financial security, health and well-being, and safety net against accidents/illness and their adverse impacts. Given the child's situation and reactions, it is likely that the frequent changes in homes have caused a sense of unpredictability and insecurity, hindering the comfort of consistent, reliable safety.