What clothing should I take in Beijing on the week of Mar 28?

Beijing is still somewhat cold currently although the days are plenty of sunshine. Yo'd better wear a warm sweater and overcoat.

Is a sweater and coat required during the days too?

During the day no need to wear sweater or coat. Just a jacket is enough. But, if you are planning to go out until night, you'd better wear coat.
Today, 26th, was warm at daylight and turned cold during night. Tomorrow, 27th, it will be quite warm during the day.
Be careful for the wind though. It's quite strong sometimes.
Have fun in Beijing.