What is a good bedtime for a 4 year old and a 2 year old?

6:30 and 7:00 are perfectly reasonable. My daughter is 3 and she goes to bed at 6:30 and wakes up at 7:00. Children in between 1-5 years old need at least 12 hours of sleep a night! So that is just perfect. It may be a little tough at first for them, adjusting to the new times, but within a week they will get used to it. :)