5 year old DD, almost 6, has real trouble going off to sleep. She finds it hard to switch off and let herself relax. Her mind seems to start buzzing once it's lights out and she's constantly getting up to the top of the stairs to ask questions such as at what age do we become grown ups?what's the unhealthiest food in the world? And so on. And on and on! I don't engage in conversation - I simply repeat good night it's time to sleep. Sometimes she looks exhausted but she doesn't seem to want to let herself go off. Once she does go she sleeps til morning. How can I help her?