The children .... They are running!

Resolution:

• 1. The correct option is aren't swimming. This is because the sentence is in the present continuous tense, and 'children' is a plural subject. Therefore, 'are not' (aren't) is the correct auxiliary verb. The phrase 'They are running!' further confirms the present continuous tense for the second clause, implying the children are currently doing something else (swimming) and then they are running.

Answer: aren't swimming