This is a question tag.
The main sentence is:
“The children are playing”
It is in the present continuous tense using are.
The statement is positive, so the question tag must be negative.
✅ Correct sentence:
The children are playing, aren’t they?
aren’t they? → correct negative tag for “are”
don’t they? → used with simple present tense
do they? → positive tag, incorrect here
weren’t they? → past tense, incorrect tense usage
