An interesting topic would be to study the progression of human develoopment framed by Maslow's "Hierarchy of Needs" or Erikson's Theory of Psychosocial Development.
Erikson's would probably be your best bet. His theory breaks child development into stages and then categorizes those stages into the child's psychosocial/developmental needs.
Also to consider-- Freud's Psychosexual Development Theory-- The title is pretty self-explanatory! Freud analyzes human psychological development through sexual needs, basically.
OR...If you wanted to go super-deep, consider writing a compare/contrast between Erikson and Freud.
I am going to include some links below on these theories that would have some good information to get you started.