In today's world, there are many interesting topics that you might want to consider. To think about this, first consider what a family really is. Is it a couple, male and female, with a child or two? Or is it something less specific? Could it be a three-generational group, with grandparents, children, and their children? What about single-parent households? Are they families? Or a gay couple, with or without children? Are two friends who have lived together for a very long time a family? Is a household always a family?
You might want to focus on one of these "alternative" kinds of families, or you could do research comparing "traditional" families with alternative versions. One area of great interest is the emotional health and happiness of children in traditional versus alternative families. Another area of interest is the effect of poverty on families.
I think that once you begin to consider what a family is, you will be able to think of many possible topics to pursue.