You should always send you child to bed at the same time every evening, if they haven't got school the next day then let them as a treat to stay up longer. My boy is 11 and he is in bed by 9pm every evening.
I pretty much agree with Dave, and it's especially important for babies and toddlers to get them into a good sleep patter.
We all have an internal, biological clock that tells us when its "time to sleep." This biological process is called circadian rhythm. See this web site for more.
Short explan: You can get your childs internal clock set by consistency of when they go to bed, and sleep will come sooner and better for them then on that schedule.
Studies show if you do have a set circadian rhythm and want to alter it, you should change it (your bedtime) by only one hour a night for a week or so, and then another hour ... i.e. an hour at time. It is when you change it by more (in long flights) that you get what is commonly called "jet lag".
Its ok to vary it once in a while (like Dave suggested) but try to keep it consistent most of the time.
Yes! Yes! Yes!!!! I work with babies, and have an 8 yr old daughter. I have seen the difference it will make.
Other people asked questions on similar topics, check out the answers they received:
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them