How To Pack It
Travel With Children
No, you don't have to pack them (tempting though the notion may be at times), but a lot of people ask about travelling with children in tow. With toddlers and smaller (who will need diapers, special food, favourite toys, etc.) it's a daunting challenge, one likely to be outside the purview of "travelling light". If you have a choice of destinations, choose those where you are likely to want a vehicle anyway (Ireland, say, or the Provence region of France, places where you will want to visit areas not well served by public transportation), and simply rent a car.
While childen are still young enough to require carrying for significant periods of time, you will want to give some thought to comfortable methods for doing so. The very young (and, some would argue, not so young) are probably best carried by one of the many types of body-hugging slings. These vary greatly by culture & geography, and are covered in some depth by the folks at TheBabyWearer.com.
Alternatively, a lightweight child stroller does not usually require checking, and can double as a shopping cart, or even luggage trolley.Finally (and even if your travels take you only as far as the local market), you should know about the more Western-style child carriers, which exploit backpack frame technology to comfortably transport young ones on your hips and (to a lesser extent) shoulders. Those who lead any kind of active life whatsoever will never regret acquiring one of these. Several companies make them, but Tough Traveler® (pictured at the top of this page) is the brand to beat; they've been building them for over 25 years. Their contact information can be found on the Suppliers page.
If you're looking for a more traditional stroller, gb's Pockit Air All-Terrain is more collapsible than most, and reasonably light in weight.
Should you wish more than these packing-related remarks on child travel (OneBag.com is hardly an authority on the broader topic), you'll need to look further afield. Olivia Meikle offers plenty of well-informed advice in her engaging Around the World in 80 Diapers blog. And the folks at Tripbase have put together a helpful article on one-parent travel with children of all ages.
Educating the Post-Toddler
Once children are old enough to keep up with your walking plans, introduce them to the joys (and responsibilities) of independent travel. This means that they should have bags of their own, in which to carry whatever they choose to bring along (in practice, this will primarily be clothing, and perhaps an item or two for amusement; the accompanying adults will already be bringing the communal needs). A modest daypack should suffice for this. It's preferable to shop for sam'rery no more than 10–15% of their body weight), their travel skills, and (one presumes) Mom's & Dad's adherence to the "if you don't carry it, you don't bring it" rule. In all cases, be sure — for any kind of major trip — to include these burgeoning travellers in your final exam exercise.
Everyone brings one carry-on. As a family we never check bags. It's just a hassle, and I like to hit the ground running.
Tales of Travelling Tots: Chronicles from the Cloud
We're a family that has been on an open-ended, non-stop world tour since 2006. We've been to 4 continents, 32 countries, & over 175,000 miles so far.
We have mastered the "family traveling light" art in spades & we breeze through airport flights, cargo ships, and any mode by which we travel. We've traveled as a family since my child was 2 weeks old, but this trip started when she was 5 and she is now 9 (and years ahead of age peers in school even though she has never owned a Nintendo or iPod).
Even when we are going through three seasons of weather for months at a time, we just carry a small daypack each, and that includes at least one laptop and homeschool supplies!
Trust me, families can travel light!! 
Simplicity can be so enriching and will also save you a bundle!
I traveled for years with two kids, often by myself. There is nothing cuter than those little ducks rolling their carry-ons confidently through the airport!
If you are going for weeks (any time over one week), you only need 4–6 of any clothing item. When kids were little, and growing fast, I'd buy 2–3 lightweight, quick-dry (convertible) pants and tops, and plan to do laundry. That, and one pair of walking shoes, one pair of sandals/water shoes, PJs, a bathing suit, a fleece, a hat, and a good roll-up rain jacket has taken them all over the globe. I'd often have these in their closet set aside especially for travel.
If you are visiting a place or family you see every year, try to borrow a corner or closet to stash stuff you'll use every visit. I have water noodles, a boogie board, lawn chair, and exercise ball stashed at my mother's Florida home). Also, we have gone to the beach, purchased a USD$2 pail and shovel kit there, and just given it to another child as we leave.
The next time you return from traveling, look at anything you did not actually use or wear, and don't bring it again.
Especially with younger kids, it is critical for them to learn to make do/entertain themselves. This is the time of their lives when these skills are learned, and once they figure it out you will never need to tote stuff for them again when you travel! Well, at least not so much.
JMHO … and advice that has worked for my two globetrotters!
When we were growing up, my parents had a strict "carry-on only" rule for themselves and the five of us kids. So we never checked any bags, even on long European trips. If we couldn't carry it on the plane, then we couldn't take it. Simple.
Additional letters from families travelling with children can be found on the TraveLetters page.