There are two types of vacations - the type where you go somewhere to do something (e.g., Paris, London, Costa Rica) and the type where you go somewhere to do nothing (e.g., the Bahamas, Florida). No matter what kind of vacation, one of my critical requirements is that a vacation be about sleeping in. To people on vacation without kids (i.e., me up until this point) the thinking is "The Louvre will still be there at 11 am, no need to be there when it opens. Let's sleep late and eat chocolate croissants as we wander our way over there later."
On the other hand, remember family vacations when you got up at some horrible hour to beat the crowds? When I lived in DC and would take the metro to work I would look at tourist families in disgust, "Why are you people up and out at 7:30 in the morning? The museums aren't open yet and you are in the way!"
Now I am starting to understand. Kids like to be entertained, babies don't know the weekend from a weekday (LP actually gets up EARLIER on weekends than school days), and you will never sleep past 8:30 am again. Might as well embrace this fact and avoid the crowds.
PS: I think this should work everywhere except Disneyworld. Everyone is up early there, probably better to go at night when everyone else is too exhausted to move. Or, better yet, don't go at all!