I will go to Hangzhou at the end of Dec and will stay at Westlake hotel. I plan to go to Yiwu Trade Centre. What is the best way to go there?

If you are referring to the commercial center in Yiwu city, your hotel is right at the opposite of local main railway station, where there are regular trains to Yiwu every day. Upon arrival at Yiwu, take a taxi to the destination. There you will find baby clothes in bulk.

If you mean the Yiwu trade center in HZ city, walk from your hotel to HZ Railway Station Metro Station to take subway line 1 to Passenger Transport Center (Keyun Zhongxin) Station and then take a taxi to the market.