we are two adult one child (6 years old) want go tianjin by super train from yiwu

As I know, there are three normal trains running between the two places and they have hard seats, hard sleepers and soft sleepers. The travel duration is around 20h.

By saying "super train", do you mean high-speed train in China? If so, it is suggested to transfer in Shanghai and you can take high-speed trains for all journeys and it takes much less.

To search the train schedule or book ticket online, you can refer to this website:
https://www.travelchinaguide.com/china-trains/