What are they doing?
They are riding bikes.
What is he doing?
He is surfing.
What are they doing?
They are playing together. / They are playing ball.
What is she doing?
She is playing computer games.
What is she doing?
She is doing gymnastics.
What are they doing?
They are playing board games.
What is he doing?
He is painting.
What is he doing?
He is reading.