I watched the raw version of the 2 last episodes but I don't completely understand. What happened to Doudou?
Jin left Doudou alone on the bridge, instead of looking for the police he started playing with a dog and must have gotten lost and kidnapped again. It was a time when there was a lot of child trafficking, especially boys due to the one-child law. They don't make Doudou's future clear, I think it's a way for those parents who never met their children to connect and understand police officer Wang.
I had hopes and wanted Xiao Qi to be Doudou. But then I thought, how would they explain the fact that he is like Bian Jie? Then I realized that there was no way Xiao Qi could be Doudou, and that Doudou wouldn't come home. Even so, I couldn't hold back the tears in the last episode. Poor Doudou.