We are wanting to visit Shanghai and Beijing the last days of February and first week of March.

Well, the first city you mentioned will still be a little and windy during that period. The average temp will be around 7C.

Beijing will be chilly then, with the average temp of around 0C. So you may need to think twice to travel with the elderly at that time, considering the weather condition.

Anyway, you can still enjoy yourselves by many attractions and activities then.