Answer: This is an example of "OBSERVATIONAL RESEARCH" about the psychological and emotional well-being of children who are maltreated.
Explanation: Observational research is a type of research study, were result are gotten from observing a phenomenon act on it's natural course, without any influence from an external body.
Observing children who has been maltreated, is an Observational research because they were no psychological therapy for the child. The child was observed and result were noted for every three years, to understand how a child who have been maltreated changes character for every three years.
This observational studies on this child will tell the researcher how maltreated children behave in their adulthood.