Children steal your sleep - it is not possible to be a parent and not have this affect the quality and quantity of your sleep, unless you have a vast retinue of retainers at your service, or are already like Margaret Thatcher1. However, at the same time, the worse your sleep patterns are, the more difficult everything else in your life becomes at an already challenging time - so it's well worth mitigating the damage. And it's in their interest too - if they are waking up a lot or sleeping odd times, they will probably be irritable and unable to concentrate - just like you - this is a potentially explosive combination. Our parents had drugs they could give to us, but they're mostly all banned now - so we will have to make do with routines, common sense and basic psychology....
For older children, this entry sets out some points about their sleep.
I've been sleeping like a baby - sleep for a few hours, cry a bit, sleep for a few hours...
– John McCain, just after losing the US Presidential election
Up to about three months, your sleep is probably not going to be great. Someone always knows of a baby that starts sleeping nights after two weeks, but this is the exception to the rule. So sort yourself out for maximum comfort - cot next to the bed, baby in bed2, baby feeds while you're asleep (breast feeding - the bottle tends to fall out of your hand...), whatever. After three months or so, you can start training your baby - spacing feeds, sleeping in their cot, sleeping in their own room perhaps. Good habits and a little bit of suffering now (you may have to sleep less while your baby adjusts) will give you precious extra zeds later.
If there are two of you, think about sharing the work - for the fathers, this doesn't mean growing moobs3, but maybe getting up to comfort a baby that isn't hungry, and of course preparing a bottle feed if that's the option retained. You shouldn't rule out the option of a night in the spare room for one or other of the parents - just to have a break now and then, or before important meetings. A solid meal or feed before the night can help minimise or eliminate waking up through hunger as well.
From about the age when they are no longer in a cot, this is the ultimate weapon of the toddler. What parent could fail to acknowledge the wail of their progeny - 'Daddy I want a glass of water?' It's a mystery to this researcher why they get so thirsty at night, but one conclusion could be that this is an acceptable way, when waking up in the middle of the night, to get some attention from one's parents. You can try putting a glass by the bed, making sure they have a drink at bedtime, but fundamentally, it's you they want...
Even when things are going well, when you've been sleeping solidly for some time, the other thing that children do a lot of is get sick. This may involve in you waking up to check up on them, because you're concerned, or waking up to deal with a bed full of vomit4. This is almost the worst, because not only are you up, you're also having to react, make decisions, deal with a grumpy/weepy/hot/nauseous child. There's not a lot you can do about it either - other than being prepared by having the appropriate bucket/medicine/spare bedclothes/NBC suit5 handy in case of need.
Monsters in the wardrobe, gremlins under the bed, nightmares, strange shadows, too dark, wind outside, rain on window, giant lobsters (yes, really): all of these are capable of generating abject terror in the average toddler to young child. They wake up and they will yell until you get there to comfort them. If you're lucky, the shouting will wake any other children as well. You can try some words of comfort 'giant lobsters live in the sea, son, not in your bedroom' or 'vampires and dragons are only in stories, and pirates and knights are only in the past6'. You can try leaving the light on on the landing, or a night light. You can try avoiding certain stories as the bedtime read7. But some nightmares are a normal part of development. If you can avoid that the child systematically comes into your bed as a response to this, then that would be a smart plan as this can be a hard habit to break.
A physiological subcategory of this is falling out of bed - fortunately, they normally stop doing this after about three, and even before it is not normally that frequent.
Babies can be sensitive to the slightest creak on some occasions, but can also sleep on, impervious to the most incredible racket if tired enough or used to it. Some sort of halfway house seems the best approach on this - it seems reasonable that older brethren should pipe down while the baby is sleeping, but at the same time if they can only sleep in a ghostly quiet, this will not facilitate an eventual transition to some form of collective childcare, and will make your life trickier as well as everyone tiptoes around the house, finger to lips.
Most children aren't capable of outlasting their parents in the evening, fortunately, but they are more than capable of waking up at a time that even a dairy farmer would consider a bit premature. Solutions include darker curtains, strict instructions on what to do when they wake up 'read your book until I come down' or clocks with eyes shut, eyes open 'if the rabbit has his eyes shut, go back to sleep'.
Part of the problem can be how long they are sleeping in the day, and when. If they sleep in the car on the way back from the creche, for example, it's not surprising that they are not going to put their head back down on the pillow on arrival. Some nurseries impose a siesta, but maybe you can influence how long it is?
The creativity of children in finding a good excuse should not be underestimated. Recent examples that this researcher has encountered include 'my pants are too tight' (at 3am), or 'I can't find my soft rabbit' (at 1am). The possibilities are almost limitless.
This is a solution, rather than a problem. Maybe even the solution. Children are creatures of habit - if most nights you feed them round the same time, and then have an endgame routine - wash, teeth, read a book, lights out (for example) - this reduces the potential for conflict, and increases the possibility that they go to sleep contented and therefore do not wake up. The constituent parts of the routine vary with age, obviously, but putting in place a routine can be done from a very early age. The downside of this dependency on predictability is that if you allow them to pick up bad habits, it makes it hard to put it right. For young children, avoiding television, computer games, boisterous activity or other over stimulation at bedtime is always a good plan.
Another angle on this is predictable behaviour when dealing with a plea to attention. One possibility is the first time you go into them, you talk to them and reassure them. After that, you just go in and tuck them in but no talk, no hug, no matter how many times they call you. They soon get the message that there's no point in calling you again. Another is - first time comfort, second time perfunctory, third time cross. For younger children, you have 'controlled crying' - leaving them for a set amount of time, then comforting them (normally without picking them up), leaving them again, etc until they get into the habit of sleeping through.
Despite all and any of these tactics, for more or less long periods of your life as a parent, none of it may work. You may just have to grit your teeth and wait for it to pass. If you find yourself really distressed through lack of sleep or the problem is ongoing, then see your GP or similar source of advice - specialist sleep clinics and the like exist for extreme cases.
For other more general sleep advice, see this entry on getting to sleep without children...