How to travel light with a family

Whether we travel for a week or a month, we pack the same thing in the same bag. My rule is each person needs to wheel their own bag the entire trip. And we travel by plane, train, bus and boat a lot. This photo above sums it up. Each child wheeling their own bag and then my 4 year old riding on my bag which we shared. That's it.
If the trip is more than a week long, we do laundry halfway through. In Peru, we booked an apartment with Airbnb.com halfway through the trip and did a bit of laundry.
In Thailand, we did a load while we stayed with a friend.
As long as you plan on doing a load somewhere, you can pack for one week.
We also pack layers. I remember when I traveled once around Europe in December and wore every piece of clothing in my suitcase. I was that cold!

Here's my packing list:
2 pairs of pants
2 pairs of shorts
6 pairs of underwear
5 pairs of socks
1 pair pajamas
2 bathing suits
1 sweatshirt
1 dining outfit
6 shirts
1 long sleeve shirt
2 pairs of shoes (you wear one and pack one)
toiletries

If you are traveling to a cold weather location, then the packing list gets a bit longer.
For Peru, we encountered everything from cold to really hot. So we had to add gloves, scarf, long underwear and a jacket.
The big issue is always whether we should check one bag and bring sunscreen, shampoo and conditioner or buy it when we arrive or even better hope the hotel is supplying it. For Peru, we checked one bag since we also needed to bring along bug spray and medications for the Amazon.
For Thailand, we bought it all there. Going to the local grocery store is always a fun experience!
The bottom line is pack light and do laundry.