What are they doing?
They're running!
What is she doing?
She's riding a bike!
What are they doing?
They're having a picnic!
What is she doing?
She's riding a skateboard!
What do YOU like doing at the park?
I like playing ball, riding a skateboard, riding a bike....
What are they doing?
They're playing ball.
What is he doing?
He's playing on the swings.
What is she doing?
She's climbing trees!
What is she doing?
She's taking a walk!