The monsters of a child

Her life changed when she learned the monster were protecting her.

But how?
They used to take over in her worst moment, when she was not strong enough to suppress them.
They would take advantage of her, scream and release their power. They would scare everybody she loved, make them run away.
She had met them a long time ago. She was little and full of joy. She was playing alone, in her word full of magical things.
Then a man, a strange one, arrived.