The children . . . . . . . . in the field now. A. has played B. are playing C. plays D. will had played

The correct answer is: B. are playing

The sentence is in the present continuous tense, which is used to talk about actions that are happening right now. The other options are not in the present continuous tense.

• Option A: has played is in the simple past tense, which is used to talk about actions that happened in the past.
• Option C: plays is in the simple present tense, which is used to talk about actions that happen regularly or repeatedly.
• Option D: will had played is in the future perfect tense, which is used to talk about actions that will have happened by a certain time in the future.

In this case, the children are playing in the field right now, so the present continuous tense is the most appropriate tense to use.