Demeter loved her daughter, Persephone very much. Since, Demeter was in charge of harvest she had to stay happy so the crops would live. Her daughter made her so happy so this wasn't a problem. Till trouble began to start when Persephone got older.
One day Hades, the king of the underworld, saw Persephone when he was with his dog. He fell in love with Persephone so he stole his niece, grabbed his dog and left. Persephone was so sad, and she wasn't the only one, Demeter was also very sad.
Persephone wouldn't eat because she had heard that if you were to eat something in Hades, she wouldn't be allowed to leave. She had to eat though, so she did. She cried and was so sad until Zeus' son, Hermes, went down and made a deal with Hades.
I hate this!
The deal was that for six months Persephone would leave and go to see her mother and for the other six months she was with Hades.
When Demeter was with her daughter she was so happy and the crops grew, this is known as spring and summer. When Persephone was with Hades Demeter was sad and all the crops died, known as fall and winter.