Question

look the children ____ （play）with the yo-yos.

Answer 1

句子有错。
如果 look 后面有标点符号，那么表示看的是正在进行的动作，后面应该是 the children are playing with the yo-yos. 意思是 “瞧，孩子们正在玩溜溜球” 。
如果没有标点符号，应该改为 Look at the children playing with the yo-yos (盯着看孩子们在玩遛遛球)，playing 是宾语补足语。

Answer 2

are playing

Answer 3

Look! The children are playing with the yo-yos.

追答

Look ! 瞧， 后面用现在进行时，孩子们正在玩yo-yos 球！

Answer 4

playing表示正在进行的状态