I'm going to have to disagree that "planning is key."
I feel the best way to travel with kids is to be flexible, play it by ear, and make sure everyone knows in advance that the trip is part of the adventure. Things may be great, and they may not. Don't worry about it and go.
As for length, don't worry about that. I park easily in places now that I would have thought impossible when I started. Just go with your comfort level. You can always get halfway into a parking spot and change your mind if it ain't working.
My advice is load up, pedal down, mind open. The rest of my life is planned enough
