Alien brother and sister

On a planet outside our galaxy, lived unknown creatures. Brother and sister. They loved to play. One day, while playing hide and seek, they hid in a spaceship and accidentally hit the start button. Since they did not know how to drive, their spaceship flying in unexplored direction. It so happened that they came to a completely different planet, something vaguely resembling the ground. But they and the ground or when not seen. With what they have to face?