Final answer:
To turn the statement 'The children are doing their homework' into a question, you would say 'Are the children doing their homework?'. This involves moving the auxiliary verb to the start and adding a question mark.
Step-by-step explanation:
The interrogative form of the sentence "The children are doing their homework" is "Are the children doing their homework?". In order to change the sentence into a question, we move the auxiliary verb "are" to the beginning of the sentence and add a question mark at the end. Interrogative sentences inquire about something and generally require a response.