I've just read an article by \link{http://www.naomialdort.com/this woman} which has cast light on the reasons why my kids go wild and run around at bedtime. It can be quite frustrating and confusing (especially for dh who would prefer them to do as he says).
In her article in The Mother Magazine this woman explains that kids know how to generate a good night's sleep by arriving in bed free of excess energy or anxiety so the wild period before bed serves the purpose of discharging the days stresses.
This makes perfect sense to me.
Sadly she loses me after this by saying parents (or at least, mothers) might consider going to bed with their children.
I often let the kids have a wild half hour upstairs after their baths and find bedtime is much easier and smoother if they've done this. Now I know why.