I personally chose to earn my BSW, because ultimately it was more cost effective to me because I was able to get my MSW in a one year advanced standing program. Also in comparing the curriculum to say a degree in sociology, I felt the social work curriculum provided me with more education and training in working with individuals, groups, families, and communities. I also feel the BSW is more of a competitive degree in finding social work jobs that are not with state government. It of course would all depend on what career focus you have, as I was more interested in medical social work as well as mental health.
One of the students in the two year MSW program had her BS in Sociology and had told me that she didn't really want to get her Masters at that time, but she was having no success with findings jobs. In today's economy, to remain competitive always go for the more specialized degrees. Sociology is a fine degree and the curriculum is interesting, but outside of "state" minimum entry level jobs, there is not a lot of employment opportunities for someone with a BS in Sociology. Someone with a BS in Sociology would qualify for state entry level positions in most states, but overall it is more of a general degree.
If your focus is children and families, and you have ideas of what types of jobs, it may not be necessary to change your major at this point. I am not sure where your career focus is, or how far along in your child and family development program you are, but I would highly encourage you to use online job searches for positions you are seeking to see what the qualifications of those positions are. http://www.indeed.com is a good job search if you have not used it before, and you can even put in the degree and you will get "hits".
If your goal is to earn your MSW, you may want to consider perhaps changing your major (again depending on how far you are into the program), because with a BSW you can save one year of time and tuition in advanced standing MSW programs. Most, if not all MSW programs offer advanced standing MSW slots.
Best wishes!