Broadway week shows

I was always wondering how is the list of shows that will participate in the Broadway week being determined. Does anyone have an insight into this? I'm asking because Moulin Rouge is not on that list, but it does participate in the Kids on Broadway night on February 25 (also 2 for 1 tickets deal). Isn't it strange since it's not a kids show (in my opinion)?

Also, couldn't help but noticing that WSS was the only show that sold out today by 4pm. It appears to do very well, I can't wait to see it in three weeks.