There is so much personality within your family, khakis and a white shirt can't quite live up to it! The best part of dressing individually is that when you come together in a single image you will still blend as a family! For your session, make sure there isn't one person dressed formally while the rest are casual (and vice versa!), and stick with similar or complimentary color families and fabrics (everyone in pastels or earth tones for example). For kids, I love to see at least of glimmer of their peronality reflected in their clothing-- a fun hat, silly shades, or even those quirky rainboots they refuse to take off !