1 Is the boy/eating/a cake? Yes, he is. No, he isn't.
2 Are the children/playing?
Yes, they are, No, they aren't.
3 Are the girls/riding/horses? Yes, they are, No, they aren't.
4 Is the dog/running? Yes, it is. No, it isn't.
5 Is the man/reading? Yes, he is. No, he isn't.