Final answer:
The complete subject in the sentence given is 'The two playful children,' which includes the simple subject 'children' and its modifiers.
Step-by-step explanation:
The complete subject in the sentence "the two playful children made up a new game" is A) The two playful children. The complete subject includes all the words that describe the simple subject, which is the noun or pronoun that the sentence is about. In this case, 'the two playful children' is the part of the sentence that includes the simple subject 'children' along with its modifiers 'the two' and 'playful', providing a full description of who is doing the action.