The young girls parents were happy to let Demeter use a room and look after her. In return she would look after their son.
A reward for their kindness, Demeter attempted to give the boy immortality by putting him in the fire each night and removing him before dawn.
Of course when the mother found out she was horrified and asked Demeter to leave at once.
That immediately made Demeter angry and exposed her true self. The family begged for forgiveness and in return they agreed to her demands. A temple would be built in her honor, and to teach the world the secret to immortality.
The temple was built and she continued on her journey.