I agree that given your interests, and with a child, that Hong Kong is a better fit. Both Hong Kong and Shanghai will be hot and fairly humid in the summer months, so not a whole lot of difference there. Hong Kong is a bit hotter and has more rain, but Shanghai has worse air pollution. But to me the bigger issue is that I am not sure there is a whole lot in Shanghai to interest an 11 year old. In Hong Kong, you could easily spend all your time in countryside areas on walks or hikes seeing mountains, monasteries, temples, small villages or beaches, or taking trips via boat (ferries as well as private hire or junk trips like the Aqua Luna, see
www.aqua.com.hk). With 2-3 days, I can think of itins where you would not do <i>any</i> shopping unless you really felt the need to do so. We also have things like the Peak Tram, the cable car to the Po Lin Buddha and Ocean Park (see (
http://www.oceanpark.com.hk) which are fun for kids. (We also have Disney, although the park is small and IMO should not be a focus of a trip for someone from the US who has access to larger Disney parks.) Shanghai is a huge city (22 million people and counting), where access to the countryside requires more of an effort and commute.
July 1 is the annual anniversary of Hong Kong’s reunification with the PRC, and there are usually, but not always, fireworks in the harbour here which are quite spectacular. If you can include Hong Kong on July 1, that may be an interesting event.
I don’t know the rest of your itin for China, but I think you can find places other than Shanghai which would fit your interests better. Shanghai has very little of historical interest (because it was not important to imperial China and was basically small fishing village until the last century) as opposed to places like Beijing or Xian which were very important centres in imperial China. While Shanghai can perhaps be interesting as showing the <i>future</i> of China, there are easily a other dozen cities which could also provide this aspect (Shenzhen, Guangzhou, Wuhan, Harbin, Ningbo, Chongqing, Quingdao and Dalian just to name a few; some of which also offer historical sights.) And Hong Kong is also one of them.