My approach when documenting families is the same as weddings. I don't see your session as a styled photoshoot.
I won't turn up with blankets and balloons and ask you to wear pretty dresses. I want to document you and yours exactly as you are and the way you interact with each other. Like all sessions you may start off being conscious of the camera but with a little direction you'll soon forget it's there. As part of my approach I will also take a couple of traditional photos.
I find choosing a location where you and your family are most comfortable works best, this includes photographing you in your own home, or heading out on a little adventure with you to your favourite park or pizza shop.