I'm currently working on my practicum as well, and it's on....childhood obesity! I can share with you some of the people / places my mentor suggested to me for hours. WIC clinics, schools, talk to dietary at the public schools, assess what types of snacks are in the vending machines. Children's Hospitals near you may have clinics for obese children and are an awesome resource. Local YMCA has great resources for kids and you could check out programs there, I've done a bit of "windshield" observation as to the type and quality of playground equipment at local parks and schools (you can only get 6 hours for this type of observation). A great place I've found to talk to parents is at McDonalds with playlands...especially on a rainy day. My son is going on a field trip all about promoting good nutrition and exercise and my mentor said I could definitely go along as a chaperone and use this as part of my hours. I found extension programs in the community (via the public school website) that assist underserved populations with dietary counseling and exercise recommendations for children. You local health department also would be an excellent resource. Don't laugh, but I even sent a few questions via email to First Lady Obama since she's very active regarding the topic of childhood obesity. If I receive a reply, excellent, but I'm not holding my breath on that one.
Talk to your mentor as he or she can offer you other suggestions.
Hope this helps!