5.5 year old DD is starting to drive me mad. Every night for the past few weeks, without fail, she'll be lying in bed after her story half asleep and will then start messing around and disturbing 2.5 yo DS and 4 month old DD2. How can I stop her doing this? She's exhausted but by the time she finally calms down enough to sleep, it's nearly 9pm so she's even more exhausted the next day. Help...