Urgh, my youngest two children are and always have been poor sleepers. One is 7, the other 4. Between the pair of them, I'm woken up probably 50% of the nights, and after so many years of sleep being disrupted, even if they don't wake up, I often do anyway and struggle to get back to sleep. I feel like a zombie most of the time.
What can be done? The 4yo wakes for no particular reason, she'll arrive at my bedside and be sent back to bed. Sometimes it's a nightmare, sometimes it's that she can't find a toy, sometimes that she wants to tell me something 
she gets no attention, sent straight back to bed.
The 7yo is more often night terrors or wetting the bed, although to be fair he's not up nearly as often as the younger one any more.
They both suffer from night terrors (as does my DH).
I'm so sick of being woken up! Last night I was up for about 3 hours between the pair of them. They were both terrible sleepers as babies but I was hoping they'd have outgrown it by now 