We notice it as well when the kids don't get enough sleep. They need a lot. We shoot for 11 hours for both, with our 2 year old tossing in a 90 minute nap midday. Plus, we have a really well defined bedtime routine that we have enforced since they were babies. Bath, pj's, brush teeth, 3 books, lights off. I think routines are really important for kids.

But it's not only for the kids. That time from 8pm on is really the only parent time my wife and I have. And we get so much done, from preping lunches to laundry to just hanging out with each other. I would really miss that time if the kids stayed up late.

This sorta brings to mind something I've noticed a lot of lately – many parents aren't paying attention to the recommended amounts of sleep that pediatricians cite. Several of our friends who have kids between 11-18 months old quite often don't put their children down for bed until close to 11 P.M. – sometimes even later than that! And some of them don't enforce a routine afternoon nap. We can readily tell when our little guy has not gotten enough rest – he's typically cranky and/or belligerent, often actively seeking to do things that he knows will net him scoldings and timeouts.