I guess it depends on the age of the kids...if the age is between 1-3, they should get about 2 naps in the day time and go to sleep at least by 9-10pm. The timings depends on how soon you as a parent want your kid to go to sleep. Make it a habit and follow it as a ritual.
"Early to bed early to rise" - it's a principle to all, kids and adults. But the most important thing is how much time your kid sleeps. Sleep plays an important role in the mental growth of a kid and many of such processes are done in brain during sleeping time in the case of a kid. So ensure him at least 10 hours a day sleep for his better tomorrow.
It is difficult to lay down rules since it depends on the family and their life style . But ideally I would say that once they begin schooling they should be in bed by 9 Pm , so that they form a routine of sleeping early and waking up early.
The correct time to go for sleep for a child should be decided on the age factor.
For infants and the children between 1 to 5 years age need a full 12 hour undisturbed sleep.
When the child starts going to school, the sleeping time should be anywhere between 8-10 hours.
These days, if I take into consideration school going children, then I will have to consider their burden of homework as well. After returning from school, children need some quality time in the evening as well. So, considering all this, they should go to bed ideally by 10 PM and if not then maximum by 10:30 PM.