Daughters are adopted from Hunan, China & would like to visit. When & where is best?

We also want to visit Bejing, maybe Guanzhou and HongKong. We feel as 4th & 5th graders now is a good time, but as advanced students it is difficult to pull them out of their classes and have them miss school. We need to be able to get a feel for the country and culture and explore Chungsha where they lived. We are figuring at least 2 weeks if not 3. Am very open to suggestions.