Spending 3 weeks in China. What are top 3 must do/see things?

Family of 5 traveling to China youngest kid is 9. We will be based out of Shanghai and we have a total of 3 weeks. Not opposed to travel by air or train to other cities. I’m looking for recommendations of things to do. Things to experience and things to go see. We really want to go pet pandas in Chengdu and visit the Great Wall. What kind of tours can we do? I’m looking for unforgettable experiences to build memories with the family.