i am coming to dalian in january, with my 20month old baby, how cold will it be

Yes, it will be cold there during January. The average temperature during the day time is about -10C. The wind is so heavy during that time. But it is warm in the house, so if you do not take your baby out, do not worry about the weather.
If have to take it out, please put it more clothes to protect it from the cold weather.